Most Helpful Girl
You are a guy, so I'll answer this xD Yes I do realize that sounds weird. But I am a tomboy, and most of my friends are guys. If you were a girl, I wouldn't touch this one with a ten foot pole. However, you'll listen and learn, so here goes.
If it comes up, gently and slowly move in. Do not go fast. Try to make sure your mouth is clean, food in your mouth, or even gum can create a gross feel. If you go slowly and she doesn't want you to kiss her she will move away. Most women keep their head relatively still however pay attention because you do not want to butt heads with her. If she tilts her head one way, you tilt yours the other. Make sure you have recently licked your lips as dry kisses will chap her lips and yours too. If your lips are already chapped, it'll hurt her if they aren't wet. Not sopping wet, and not with a lot of slobber. Moist like cake :).
Gently touch your lips to hers, don't open your mouth at first just press gently against her. If its both of your first kiss its likely to be awkward and you might not like it the first time. Breathe through your nose, not your mouth. Lift your head up to gauge her reaction. If she is shy she might not do much, if she's bold she might touch you, or pull your head back down to her. When you go back in to kiss her again just press softly. Not to rough. Gentle pressure. You'll feel it building, and you can follow it naturally after that.