Most Helpful Guy
The first thing I notice in a girl, is how good-looking she is. She will have something about her that will catch my eye, be it her pretty hair or hairstyle, face, or even what she's wearing (for example, if she wears something with cleavage, I'm gonna notice her). Depending on how gorgeous a girl is, she might stay in my head for as long as a few days.
Aside from that, there are a few other ways that girls leave a good impression on me:
-Telling jokes. Girls who tell me jokes easily stand out from all the others, because it shows me she's got enough confidence and/or doesn't care about what other people will think of her too much. Girls who try being funny regardless of whether other people will find her funny or not, will always interest me.
-Girls who take what I say, and follow up with something sweet or naughty. For example, if I tell her I'm going to shower, she might go: "Oh, can I come with you?" I DON'T CARE how corny/cheesy it sounds! I'll be A LOT more interested in a girl who says something like that, than one who doesn't do it.
-Girls who like video games. That's an easy one. And I don't mean just the recent video games. If a girl walks up to me and starts talking about Mega Man, Donkey Kong, and Legend of Zelda, I'll be down on my knees before even considering if I should marry her or not.
There are a few others (like how sexual a girl is), that I won't really get into much detail.