Most Helpful Guy
Well first things first, she has to be approachable and relaxed. There's nothing that will make a guy more likely to bail on meeting again than feeling uncomfortable like she doesn't want to be there or doesn't want to be around the guy. If she is quiet and standoffish, why would I want to put myself through that again? I'd probably more than likely feel like we just don't have any chemistry if she came across that way. So smile and don't be afraid to talk. It's okay to be nervous, just don't end up coming across cold as a result.
Next, it's really going to depend on the guy. For me, and this is just my personal preference, I want to see some signs of intelligence. I think intelligence is probably the most important trait for me. If she shows that she's a thinker, regardless about what topic it may be, just the fact that she shows she's got depth to her thoughts is a big turn on.
After that, sense of humor is the next big one. I have a distinct style of humor, and while most people appreciate it, some do more than others. I like being with somebody I can really let loose with and not feel like I have to censor my joking nature. If I feel like we aren't on the same page humor wise, I often end up not saying things that might come to mind. That's fine for a friendship or somebody I hang out with occasionally, but when it comes to a romantic partner, I want to be with somebody that really gets me so I don't have to hold back.
Then obviously you have the looks department. As long as you're not ugly and there's some physical attraction you're in the clear when it comes to me though, so that's not really a big deal. I don't care how good looking a girl is, just that I am attracted to her. If I find her attractive, it doesn't matter if she's the girl next store or a supermodel, looks don't really play a role beyond that.
From there it gets notably more obscure and varies from guy to guy. I know that her having hobbies and being passionate about them is a huge plus. I like a girl that has a lot to say, but doesn't go overboard and dominate the conversation (after all, there are two people to a conversation). I definitely hate when a girl starts relating everything back to them. Like if I open up and say something in regards to how I think or feel about something, I don't like when a girl constantly immediately turns the conversation towards her. It's one thing to try to relate to somebodies story by relaying your own story of a similar nature, but it's quite another thing to feel as though she was just "Waiting her turn" to talk, and you could have said just about anything but she still would have immediately went to what she was going to say. Definitely don't do that.
I could probably go on and on, but you have to realize all guys are different. Some guys it's simply going to be a swing and a miss no matter what approach you take. Try to be yourself and make sure the guy has some idea who that is by the end of your first meeting.