Ahhhhhh..... that ever important first kiss! Well first of all be natural. Don't plant your lips on her hard and don't stick your tongue down her throat. Don't open your mouth so wide it looks like a train could be coming through any minute,and don't slobber and drool all over her! Make sure your breath is clean,no food in your teeth, that you smell nice, and start slow and gentle. Relax your lips so they're soft. As your faces are coming together(this is where you might bump noses, because the first time you don't know if she's going right or left. No big deal and it can be a tension releaser cause it will probably make you both chuckle), part your lips some and softly kiss her. From here nature will take over and you'll be fine. Also pull away gently but not too far and for a moment look at her in the eyes then come back in and continue kissing her. Don't worry about the effects of what kissing will have on your privates, it's natural for you to get an erection and it's a compliment to her. If she should notice and ask (which I doubt) just tell her it's because she's so beautiful.Oh yeah! Don't forget to breathe!
P.S. When you are ready to go further be smart and never have unprotected sex! Under no circumstances ever!