The question says it all, I'm going to try and keep this open to all sorts of things about a guy e.g his character, his personality, looks etc
Most Helpful Girl
The very first thing is his face. More specifically, the symmetry of the face, the eyes and the nose. Lips, ears and other features are measured differently depending on the guy.
Then I notice his body. I prefer a nice athletic and toned body with nice legs.
Once he approaches me (or I approach him), I notice his voice. A perfect voice would not be too high-itched.
After all of that, I go to the personality. Upon first meeting a guy, I base my judgement on whether or not to try to date him off of the first impression (funny, boring, mean, etc). I tend to go for the funny guy who seems sincere and kind. I am not at all into "bad boy" types.
But if I had two guys who were nearly the same or somehow equal (personality) in my mind, I would break the "tie" based on looks (especially face--not so much body).1