it is hard to believe that aliens living so far away from us would resemble humans, if not even the monkey, our cousin here on Earth, resemble us that much.
We cannot imagine what an intelligent being that lives millions of miles away from us (and has no affinity with humans) would look like. But it certainly will not have a human face. > Blockquote
I think there is a fine line to tread if you want to aim for “realism” vs audiences being able to tell emotions etc., vs being creative. It’s interesting to me you say monkeys and humans look different - to me, they are very similar. We share the same support system, organs, tissue covering, eyes, hands, muscles, etc.
There are good reasons to expect life to have some similarities in form simply due to physical laws and efficiencies. For example, some form of symmetry is often helpful to basic functioning, and during development. A support system for tissues is required, otherwise you have a round blob. This might be bones, an external skeleton, fluid bladders, etc. But it’s still there. Eyes, if present, will undoubtedly reflect their required use. Likewise teeth or mouthparts will show adaptation to their ecology.
Knowing these rules can also help with design of new creatures. For example, in our nature trifold symmetry (3-way) is very rare, having been seen only some extinct fossil lineages. I used this as a basis for my creature in “Feeding tubes” (Feeding Tubes). Maybe it’s not good art, but it sure looks weird. 5-fold symmetry is not rare (think starfish) and bilateral symmetry is common (everything from insects to humans).
Adding fly eyes for example is strange if you want to model a predator (why would it have monocular vision?), or a species that requires good eyesight. Compound eyes are physically limited in resolution simply due to the physics of light bending, for example.
In the same way that maths is probably similar everywhere you go, basic biology is also likely to follow certain common constraints. If you wanted more info on some of these ideas you could look into the work of D’Arcy Thompson (1917), or the more recent morphometrics research. As a small caveat, I should say I am probably more likely to spot these things than your average person as I used to be a biologist. It depends on how grounded you want your designs to be, and who your audience are.