Meeting new people for friendships and dating is a little scary to most people. Boys especially seem to have a difficult time approaching a girl to get her phone number. They fear getting tongue tied, saying something stupid or even being rejected completely by the girl. If you approach in the right way, the chance of successfully getting the girl's number increases. The secret is all about perspective from the girl’s point of view, letting go of anxiety and being confident.
Visualize already talking with the girl. Take a few moments to see yourself successfully approaching her for a phone number and talking with her. Have a basic idea of how you intend to approach.
Look at her surroundings. What is she doing? Paying attention to the surroundings, what she is holding and her activities will give you clues to possible approaches. For example, if the girl you are interested in is in a store looking at posters, she may be interested in pop culture or art. Thinking of a couple of small-talk topics before approaching prevents drawing a blank once you say hello.
Forget about using a pickup line. Never walk up and say something corny such as, "You must be tired because you have been running through my head all day." Girls usually hate that, and they've heard them all anyway. Approaching like that will get you rejected almost every time.
Approach the girl casually and make a comment. In the case of the poster example scenario, you might say, "Some of these posters are more like works of art. Do you like these colorful ones or the muted designs best?" Apply any comments to the actual situation at hand. The poster situation is only an example.
Listen to what the girl has to say. Use her answer to your initial comment to lead into other comments or questions. Show an interest in her answers and talk more about her perspective in the ongoing conversation. If it seems to be going well, say something like "Oh, by the way my name is..." and tell her your name. At this point, if she is enjoying talking to you she will answer with her own.
Decide at some point, if things are going well, to ask for her actual number. Tell her you've enjoyed talking with her and ask if you can give her a call. Have your cell phone ready or paper and pen to take the number.