Here's what I notice:

1. Race- how can we not notice it.

2. Clothing- this includes accessories and shoes.

3. Hair- I have a habit of checking people's hairstyles out.

4. How they talk- Do they have an accent, are they using broken english, are they loud and obnoxious, or timid and soft-spoken.

5. How they carry themselves- how they walk, behave, do they carry themselves as if they are "better" than everyone else, do they appear shy... you get the picture.

6. Their acquaintances- who you hang around says a lot about who you are (to a certain extent).

7. How other people react to that person- hey someone else may know something I don't.

8. How do they react towards me? Do they smile, roll their eyes, glance away really fast, look intimidated, heck, do they even notice me (just kidding).

9. I can't think of another one at this point, but I'm sure something will pop up in my head.