Okay'''
I'm not teaching you how to become a girlfriend snatcher, but we're going to work together in making you irresistable for that girl you like, regardless of her present love life.
Just be prepared and let's go....
1. Start to talk with her. Get more closer each day. Become good friends each day. Develop a free communication without pushing too hard. Just don't rush this step, as it's very important.
Girls like guys who are easy to talk to. Guys who can sit and listen to all their crappy girly talks without changing the orientation of the conversation. Be that guy, and you're going to beat her boyfriend down.
She might even begin to wonder why is she not in love with you..
2. Spend time together and increase the time gradually. Hanging out together increases the feel of togetherness, makes her feel relaxed, and creates the path for free flirt.
3. Discover your compatibilities and work directly towards increasing the bond. Suggest a project together. If it's sport, schedule a training session. Just create a reason to hang around together, a reasonable reason.
4. Do not ignore her presence. Even if you're with family or she's with her family, say hi and move on. You may not stay around her this time to avoid being too clingy and all obvious.
5. Flirt with her nicely and polite. Don't just do it like a plan. Do it like it's a moment to do it. Don't do it too often. The less, the more the feelings stay.
6. Compliment her personality, then with time, her appearance.
7. Go out of your way once in a while to impress her. Don't do it, if it will make you look like a jerk. Don't attempt it, when it means you have to neglect your important self, and she knows it.
Before you start implementing these tips, just make sure it's worth it, chasing after someone who's already taken.