Good ways to distinguish non-human characters but still have them look good?

Eyes, and voice. Also most non-human characters usually never look good with hair. As in head hair. Fur is an exception though.

Think about it for a moment....

Your alien (non-human) can be technological or non-technological. This will determine their overall body shape, more than anything else.

Technological means they have something like hands (possibly tentacles) with which to manipulate their environment. It means they have certain kinds of needs, and, those needs can give rise to both virtues and vices. Those virtues and vices would be very similar, regardless of the societal set-up, to those of humans. There would be a place to store knowledge, experience and skills -- like our heads, but it could be in the chest or other protected place on the whole body.

There would be sensors -- sight, sound, smell, touch, taste. Sight and sound are better well off the ground, while smell and touch are lower down -- maybe the sexual apparatus is also the feeding input area.

Non-tech would mean something like paws or hooves or similar. While the sensors are similar, the brain part has less need for protection, since memory is almost always overridden by instinct, hence less need to learn skills or carry knowledge

Start with these basics, and you can construct a creature that will fit your story.

Think of physical features that make up a humans physical appearance. Now think of the things that would look 10 times more attractive on a human but allows them to no longer be defined as human. Examples: fangs, horns, etc.