First of all, remember that hardly anyone is good at dating. Dating can be fun, but most times is awkward and a bit stressful. You really put yourself on the line when you risk asking someone out. No matter what their gender, you risk rejection and embarrassment.
Im going to suggest you change your outlook a little. Why not slowly let people you trust know that youre bisexual. Instead of asking a girl out on a date, how about you spend some time to get to know someone you like. Hang out with her while other friends are present. If you think you like her, invite her to do something alone with you, like coming over to watch a movie or going to a high school basketball game. As you get to know her better, bring up the topic of homosexuality, to see how she feels about gays and lesbians, if she knows anyone gay or bisexual or if shes ever been attracted to a girl herself. Check out these tips for talking about being lesbian or bisexual with your friends.
Is there chemistry?As you get to know her better, youll sense if there is chemistry between you. Then you will have a better sense if you should ask her out or not. Good luck.
You also might want to see if there is a gay/straight alliance or gay youth support group in your area. That can be a good way to meet other teens who will at least be open to being asked out by another girl.