god you guys are all giving this kid the wrong advice, you want real advice ill let you know whats up.
listen, first off BE YOURSELF, if they dont like you for who you are you'd better forget them cause you have no chance. now after talkin to a girl for awhile, give her subtle compliments about her, women love being complemented. When your around her, try not to always go over right away and say something. Kinda ignore her for little, see if shes interested. If not she may be doing the same thing to you so just play it cool. Lastly be flirty with her, joke around. One thing I always do is when were jokin around with each other, ill just grab her side a lil bit on her stomach. Now it's not much, but they like being flirty like that.
Now im 22, i forget what it was like when i was 13, but these things should work for a guy at any age. you need any other help kid, PM me. to tell you the truth most these other dudes dont know what they're talkin about.