When you like a girl, it can be difficult to be around her without making a babbling idiot of yourself. Naturally, you want to flirt with her, but you don't want to be too obvious about it in case she isn't attracted to you. Flirting allows you to test the waters without putting yourself on the line. The key is to relax and be yourself--you want her to like you for who you are.
Smile. A simple smile can go a long way and it doesn't seem like you're ogling her. Smile at her when she walks into the room. Smile when you're passing each other in the hall. It's friendly and it doesn't necessarily signal that you like her.
Make eye contact. When you like a girl, you may have a tendency to look away when you happen to catch her eye because you're embarrassed. Looking away causes you to miss opportunities to say hi or to flirt a bit. When you see her, make eye contact, smile and nod your head to say hi. This shows that you see her and care enough to reach out.
Find a common interest. If you don't have some common interest--whether it's doing the same activity, working in the same place or hanging out with the same crowd--it's hard to flirt without being obvious. You will have no way to talk to her without going out of your way. If you're in the same club as the girl that you like, though, you will have more opportunities to socialise with her in a non-demanding situation.
Talk directly to her. You want her to feel like she's the only person in the world when you're talking to her. To do this, be sure that you are actively talking to her and listening to what she has to say. Don't let your eyes wander around the room, which makes it seem as though you are looking for someone better.
Relax around her. This can be difficult, but if you're nervous, it can signal to her that you like her and that you're flirting with her. Before you see her, try taking some deep breaths to help you relax. If you catch yourself tensing up, just remind yourself to relax.
Remember the little details. Pay attention to the things that she says and use them in a conversation later. This is a flirting technique that will show her that you pay attention and that you are interested in her.