There has been a lot of thought and discussion on that point.
One of the conclusions that people like to point out is that the human version of symmetry, two eyes for binocular depth perception, two arms for manipulation, the legs for ambulation, a single sense organ cluster located extremely close to the brain... all of these factors simply add up to the best design possible.
That being the case, evolution on other worlds would probably follow the same rules and come up with a dominant life form that would look pretty much similar to what we developed into.
For years, science fiction writers have been trying to come up with believable aliens that look “alien”. Different senses, different ways of getting around, etc. They haven’t had much luck.