So, um, hi. I hope I'm not invading anyone's space by posting here since I'm MtF. Anyway, as a guy (or at least a not-quite-ex-guy) with some experience in this matter, I might be able to help. Is that weird?
Anyway, the advice to be yourself is great. A good personality will always show through. You don't want to be too open right up front, though. A mysterious guy is a desirable guy. Always worked for me. Don't lie or deliberately hid things, just don't tell her your life story in the first five minutes.
Second is confidence. It doesn't have to be genuine. At least not at first. You can get away pretending to be confident. Once you get better at pretending, you'll realize you aren't pretending anymore. You have to act confident to be confident. It's sort of like the difference between knowing the path and walking the path, Neo.
Personally, try something unexpected once in a while. It can work. If there's a girl working the cash register at a bookstore and she wants to upsell, ask if her number comes with it. I did that once and had to pay $10 for a girl's number, but we went out for about a year and a half. And it was a good year and a half. I'm not saying this will work all the time, but it's worth a try. The worst that happens is that you embarrass yourself. The very worst. And even when that happens, the odds of ever seeing that person again are slim, even if you shop there regularly.
Now if you act confident while doing this, even a rejection isn't embarrassing. She might say something like "I've got a boyfriend." and instead of stuttering and looking like a jackass, you let it roll off you like water on a duck. You say, "Too bad" or something like that. Finish up, play it cool, and end with something like "See ya 'round". Easy. Don't look let down, or bummed out or whatever if you get rejected. Above all, stay civil, stay cool. Easy. Think cool. It's the difference between Brad Pitt and Edward Norton in Fight Club.
Other things that always worked well-- let the girl do the talking. People love to talk about themselves. Ask a few questions and instead of being a non-talker and boring you become a great conversationalist. It's all in the perception. Ask how long she's worked wherever. Does she like the job? Who's the biggest jerk she works with? What's the lamest thing a customer has ever done? People have tons of stories like this. It keeps things moving what nary a lull in the conversation. Let the conversation direct your questioning. Easy. Lots of eye contact helps. If she's cute, this one's a piece of cake.
Just like voice training, there's several things that you might need to adjust. It's best to work on doing only one or two things at a time until they become more natural otherwise you'll just feel overwhelmed. I'd recommend working on confidence first. It's going to be the first thing she'll notice.
Of course there's no substitute for the experience of actually going out and talking to a real girl, so get out there. You are bound to be rejected, but that will only get to you if you let it.
