Too general brotha. Is she a friend of a friend, classmate, other? I still get nervous about asking a girl out that I like just because of the chance of rejection. Simply, ask her to do something you both have in common. See where it goes from there. If she's a classmate, just try asking to study together. If she's a friend of a friend, get together with her group and socialize. You don't have to try and be unique, I feel like a girl can sense if you're trying, especially when you're trying too hard. Just be yourself (I know it's cheesy and cliche' but its true).
Just talk to her, maybe get a little touchey feely, you know, flirty shit. Make her laugh, then when the time comes, be smooth as shizat and wham bam.