Hey Man, I am a fifteen year old magician so I understand what your talking about. One thing I have learned from doing magic is the best way to get better is to go out and actually perform. That being said, don't take this the wrong way, when you look back on it in 2 or 3 years, you will realize that at this time you suck. It happens to all of us. 2 years ago I was AWFUL. But the reason i was awful is because its in perspective to how good I am now. And i am 100% sure that in 2 more years, I will look back on how good i am now and go "damn I really sucked."
The only way to get better though, and to eventually realize I wasnt so good back then, is to improve, and the best way to improve is to go out and perform.
I have two favorite approaches are - 1) just be honest. go up to them and just say I am out here looking to show people a good time and see if they want to be entertained. Using this approach however sets you up for rejection if they are not interested, so dont get discouraged by rejection
2) is I flourish or do multiple card springs. The card spring is the most well known flourish to laymen and therefore if they are interested, they may ask to see it again or they will look at u funny. If they look at you funny then engage in conversation, tell them you do magic as well, and most likely they would LOVE to see it.
Good Luck and let us know how it goes
K