Most Helpful Guy
I'm going to give you an answer I gave somebody else on the exact same topic since it applies here.
We'll first thing is looks. If I'm not somewhat attracted, usually dead in the water. Not exactly fair, but guys are definitely visual and if they don't care for what they see, first impressions are a b****. Next would be whether she's flirting or not. If she's coming off very cold, that isn't going to build any attraction on my part.
If she has the looks that have me at least somewhat attracted, and is flirting, that's usually enough to take it to the next stage. Conversation. From here I'm looking for attitude in terms of how kind she is. If she's cursing, using slang, acting like "I don't care what people think of me" (you know these people. They think being an asshole and being "real" translates into being interesting or cool), then I'll lose interest pretty fast. I'm looking for maturity and intelligence as well. I want to know she cares enough to make a good first impression with somebody she doesn't know yet.
If she comes off as intelligent, mature, and a good head on her shoulders, that brings me to the next stage which is asking her out. On the date I start looking for more in-depth personality traits. Her level of ambition and direction in life. Goals. Hobbies. Type of sense of humor. The outside aspects that most people use to describe her.
If she's still appealing to me at this point, that brings me to the next stage of getting to know her, the most important one. The little quirks that make her an individual. Nobody can tell you what a guy is looking for here because every guy is different. It's the little things that make him go "Holy hell, I'm falling for this girl" or "Ya know, she was interesting, but now I'm starting to find her pretty annoying." This is the time where the guy either breaks it off, or gets serious about the girl he's seeing. But it's definitely an individual taste at this level. You can be the smartest, most beautiful, most flirtatious, most entertaining, funny, caring, gentle girl he's ever met, and he might decide it's not going to work out when he reaches this stage.
Hope that gives an idea of the process that goes down, from my point of view at least.