confidence but when i say confidence i dont mean for you to always try to show off or blab about your accomplishments because that is annoying. i mean that a guy has to be comfortable with himself. he can be himself anywhere he is and not be afraid to speak up or laugh out loud.
some guys you can tell they are shy or insecure or really care too much about what people think of them. you can see it in their posture and hear it in their voice and these type of guys are not fun or interesting.
If a guy doesn't have 'hot' looks, just like any woman, there's not much really you can do habit-wise to look hot. However, some things matter - confidence, being fit, dressing well, being talented/smart. All that said, sometimes, when we're friends with someone, we go beyond looks and love the person regardless.
Of course the whole confidence thing, but for me, when a guys genuinely nice, THAT'S hot. It's a bit cliche, I know, but it's completely true. When a guy has a good personality, can make me laugh, smart, all that stuff, appearances don't matter as much to me.
However, if we're talking strictly physical appearance, being fit and dressing well are always good. And smelling well, hygiene is important.