Think of the event as less of a date and more as a fun night out. If you approach the date with the goal of trying to impress her, she is going to notice and sense desperation. Rather, think in practical terms; you are going to have a drink with someone you want to get to know. She may end up dating you or you may end up making a friend. Either way, focus on having fun just as you would on your nights out with your friends. This will make you more calm and laid back, which will make your natural charm come through.
Show some mystery. Don't tell your date every single tidbit of information about yourself. If he knows a few things about you, but still wonders what else there is to learn, then he will likely find you intriguing. Tell him a few key, positive things about yourself but save most of your childhood stories, adolescent awards, crazy family members and college dorm antics for later.
Smile and laugh. Be positive. Don't talk about how you hate your job or that your roommates are a drag; the odds are your date gets annoyed with her job from time to time and her roommates probably frustrate her, too. Positivity is attractive.
Compliment him a little bit, but don't heap it on because you can make him feel awkward and uncomfortable. Rather, just give him one unique, sincere compliment that leaves him wanting more compliments. Tell him something specific, such as "that red shirt is a really nice color on you," or "you smell absolutely wonderful."
Ask questions about your date's life, job, and hobbies, then take the time to listen to her answers. If you give her a chance to talk about herself and actively listen by rephrasing her answers and maintaining eye contact, you will make her feel valued and important, which can lead to a second date.
Be yourself. Your date can probably smell phoniness a mile away, so don't agree with things you wouldn't otherwise agree with and don't conform to who you feel your date wants you to be.