1. That most ETs would look almost exactly like humans, perhaps with unusually shaped wrinkles on their foreheads

Or with a slit on his nose, and unusual patterns of hair

You'll notice - that normally the eyes, eyebrows, and mouth don't get changed.

It's understandable, as a movie trope, because we need to be able to read the expressions of the aliens.

If they had faces like sheep, or parrots, then hardly anyone would be able to read emotions in their faces, and it would be hard to recognize individual characters also especially if of the same species - just as most find it hard to tell two sheep apart by their faces if they are of the same species of sheep - would make the movie maker's job far harder.

However, the chances that ETs look more like us than chimpanzees, never mind parrots, octopuses, dogs, sheep, or any other animals on Earth, must be infinitesima

I do like the Star trek movies - but as science fiction not fact.

The movies later came up with an explanation of it, that the present day humanoids all originated from an ancient humanoid 4 billion years ago that seeded the oceans with genetic material that lead inevitably to modern humans - and similar often interfertile humans on other planets - all arising around the same time period.
Humanoid

Michael Daniel talks about a few memorable examples of non humanoid aliens in a comment so - it’s not always, but just very common. I’m a Doctor Who fan for instance and though they have many humanoid aliens, including the Doctor himself of course, so similar he passes for human, they do have a fair number of memorable non humanoid ETs that look nothing like humans.

2. That if you travel slower than light you see the stars changing position as you move

Television Tropes & Idioms

That's what you see from the USS Enterprise even at sub light speeds.

Instead - that can only happen when you go faster than light - even at speed of light you'd travel years before you noticed any changes except for the very nearest stars and even those would take weeks or months to change position noticeably.

You would see some motion of the stars yes, but not as in the movies. As you approach the speed of light, all the stars seem to move forward and gather together into a single bright spot in front of you, and blue shift to become extremely bright and hard radiation such as gamma rays.

For the stars to move past their windows in real time, they’d have to be traveling at light years per minute. At that rate it would take just a few weeks to cross the entire galaxy (at one light year per minute it would take a couple of months), not the many years of the Voyager projected time to get home. And the nearby stars would move faster than the more distant ones by parallax.

Since all the visible stars, most of them hundreds of light years in distance, move past the windows, then that makes their speed hundreds of light years per minute, in which case they’d cross the galaxy in less than a day (diameter of galaxy 100,000 light years). Even at warp speed, in the Star Trek movies, Voyager was projected to take many decades to get back home, but if they traveled only at sublight speeds, and moved past the stars as fast as this, they’d get back within a day.

3. That ETs would be biologically compatible with humans and able to eat our food, which would also taste the same and have similar biological effects.

A Primer to 'Star Trek' Food and Drink

Chance that the food would taste at all similar to them, surely infinitesimal.

Chances that ETs would be based on DNA just like Earth and able to eat Earth proteins at all must be infinitesimal unless they actually are related to us genetically.

And - if they have microbes like we have - but based on different form of DNA, i.e. XNA - in experiments on the Earth we have to be extremely cautious not to create XNA based lifeforms that could survive in the wild. Worst case is -that they could turn out to be better than DNA at surviving in the wild and take over from DNA.

So, similarly, every time the Star Trek crew beam down to a new planet - they run a serious risk of introducing DNA to the planet that might well wipe out all life on that planet. Or vice versa, if that didn't happen, then the XNA microbes returned from the planet might well wipe out all DNA on the starship.

What did the Earth microbes do to this planet - which has probably never seen DNA life before? What did the XNA of the planet do to the Earth life?

Actually there is a possible explanation in Star Trek mythology - again based on that idea of a progenitor humanoid of why we have all these similarities Humanoid

But even so - even if you accept the idea of identical DNA in planets tens of thousands of light years apart spread by some pro-genitor humanoids - why have the microbes in the different planets also co-evolved so that no microbes in one planet are harmful to any of the other planets?

Anyway whether it works or not within the Star Trek fantasy mythology - I think pretty unlikely to happen in reality, that ETs originating on planets light years apart have the same DNA and can eat the same foods, and visit each other's planets and not bring foreign microbes with them.

The closest to this in movies I know of is perhaps War of the Worlds - where the threat is a microbe that is able to infect the ETs - not impossible but probably one of the less likely of the various ways that alien microbes could wreak havoc on us or vice versa.

4. That ETs would be at a similar level of technology to us. Let’s make that a bit more specific - that their technology level would be somewhere between the technology of Neanderthals and the technology we may have 50,000 years into the future.

That’s vanishingly unlikely. Even in our solar system. One of the most habitable places in our solar system is Europa’s ocean, in our own solar system. With an oxygen rich ocean, there may be some small chance of a civilization of non technological fish or octopuses or some such. If so, then even though it formed around the same time as Earth, the chance that any civilization there is just a few thousand or a few hundred thousand years old must be tiny. Chances are, either there is no civilization there, or it is millions of years old. That’s just in our own solar system.

Now add in that our star was by no means the first star that life could evolve around. Their star could have formed up to ten billion years ago. And now they are supposing that they are at the same technological level as us, i.e. their development so exactly paralleled ours that there are many civilizations at the same level of technology we have in the 21st century, not the nineteenth century or the year 3000 or whatever. What’s the chance of that?

The Star Trek universe they explore is obviously a young one, with

I know that it’s the assumption in many movie plots, but it requires a lot of “suspension of disbelief”. In the Star Trek universe they hypothesize “ancient humanoids” that seeded many planets with DNA so designed that they would all evolve to civilizations of humanoids with space faring technology at around the same time, to within a few centuries, 4.5 billion years later.

Ancient humanoid who in the Star Trek universe seeded many planets with life which independently evolved to humanoid lifeforms which then evolve space faring technology within a few centuries of each other 4.5 billion years later

That maybe works in fiction, but in reality, the idea is just absurd.

So they would be likely to be a millions of years old civilization. Either they have no technology (e.g. in an aquatic dolphin society, or even the likes of clever parrots, able to do some manipulation of objects but not to the extent we can), or they have millions of years old technology. If nearly every star has a civilization, there may be a few at similar levels of technology to us, but the number must be tiny. You can do a calculation to figure out how many.

So - you have to feed some numbers into it, but let’s say that civilizations have been possible for 10 billion years, and that it takes 5 billion years on average to evolve to a civilization on a planet, similar to Earth. That way you’d end up with lots of civilizations. How many then would be at Earth’s level of technology, or close to it, say as advanced as the Neanderthals but not as advanced as 50,000 years into our future. That’s a 300,000 year timescale. Then, assuming that evolution to technology is easy so we have lots of civilizations evolving for the last 5 billion years and that the distribution in time is random, one civilization in 16,000 of the ones with technology would be at a similar level of technology to us. But just about every civilization the Star Trek crew encounter is at this level. All the invasion movies also involve aliens at similar levels of technology to us.

Of course if they all became extinct soon after reaching our level of technology that would be different. But that’s not an idea explored in the movies, and I think it’s implausible myself.

See also:

• my answer to If we found a habitable planet but it already had sentient inhabitant, would we try to conquer it?
• my answer to Does the astro or geophysics of Earth create an upper limit to the size of an alien being that could physically land on Earth and travel our surface?
• Case For Moon First - habitable exoplanets

5. That stars and planets are much closer together than they really are. In Star Trek again, often you have boundaries between multiple star systems that are defined to the nearest kilometer - you move your ship just a few kilometers, even meters, and you find yourself in “Klingon territory” or whatever, light years away from the nearest star. They drop out of warp within a few kilometers of another spaceship. When they give distances to things, it’s always a few hundred or a few thousand kilometers. In reality, the distance from Earth to Moon is over 300,000 kilometers, so they rarely are as far away from anywhere sublight as the distance from Earth to Moon. Distance from Earth to Mars at closest is more like 67 million kilometers. Mars At Closest Point To Earth in 11 Years May 30, 2016 - Universe Today

CONVERGENCE OF FORM FOR INTELLIGENCE

You might wonder if ETS might all look similar because of some convergence of form, like the way that fish and dolphins look similar.

However, most intelligent animals on the Earth are - apart from Humans - Chimpanzees true - but that's no surprise as they are related to us. But also

• Parrots
• Whales and Dolphins.
• Octopuses - and quite possibly Giant Squid
• Elephants
• Slime moulds can solve puzzles and show an intelligence of sorts
• Ants and termites are able to make complex constructions, and though not particularly intelligent - even as a colony - may be on a separate evolutionary path to technology - at least speculated in sci. fi. stories

Of those, the Chimpanzees are not necessarily the most intelligent. Some think parrots are most intelligent, which is why I listed them first.

If you looked at Earth say ten million years ago before emergence of modern humans or early hominids, you wouldn't necessarily pick out primates as the ones most likely to evolve intelligence.

You do get convergence where it is needed for something to happen. Bats and birds both have wings, in both cases two roughly similar (though some dinosaurs had four wings as do many insects of course).

Perhaps in the universe as a whole, in Earth like atmospheres nearly all flying creatures that have wings - though you do have alternatives in princile such as creatures that use hot air or gases like hydrogen to fly.

Dolphins and fish both look similar in shape. But again, squids can swim, and so can jellyfish, in their own way.

Eyes come in a small number of different forms - but with some variation including compound eyes.

It does seem likely, from our Earth - that Earth like planets might well have recognizable "fish", and "birds" and that there may be many creatures with eyes that look like animal eyes.

Intelligence though - this seems to come in many different forms. There doesn't seem to be any particular pattern to it, so seems unlikely that ETs would even closely resemble us.

If technological, they need hands or tentacles or something of that sort, and need to be reasonably strong. But you can imagine many ways that could happen. If parrot like for instance they'd need extra grasping limbs or tentacles to hold onto things, or very agile and strong feet. Octopuses could do with tentacles that separate out into "fingers" at the end perhaps. Similarly Elephants could evolve fingers a the ends of their trunks.

And dolphins - need something - tentacles, fins that can operate as hands or something like that if they evolve technology like us.

Binocular vision would also help.

Non technological but intelligent and civilized ETs wouldn't need to have any of those.

And - they could be as different from us as the slime moulds, somewhat intelligent, surprisingly.

And ideas to use them to make computers
Growing Computers from Slime Mold

EYES AND EXPRESSION

For that matter, also eyes - all the movie ETs, even ones that are not supposed to be related to humans at all - they have eyes that are astonishingly human like except, sometimes, for eye colour. They look more like human eyes than the eyes even or sheep, or dogs, or cats.
 
Human like eyes pretty unlikely you'd think as no other animal has eyes that look quite like ours except Chimpanzees.

And nearly all ETs in films will laugh and smile when happy - almost no animals except humans do this.

It seems extra-ordinarily unlikely that ETs would be so similar to us that they bare their teeth when happy (for many animals that's a clear sign of anger) and make laughing sounds that resemble ours when they hear a joke.

But of course they need human like eyes and mouths, or it would be almost impossible for most people to read the expressions on their faces.

Other ET ideas in films make more sense. For instance when ETs make themselves look physically bigger when angry or defensive - extend spines or in other ways make themselves seem larger - that I find quite plausible. A wide range of creatures on the Earth do that. So if we are a good analogy, might well be many ETs that do the same. It makes logical sense also.