Relax. Believe me, it will come naturally and it's fun.
Here are some tips:
It's best to kiss with your heads off-set at an angle.
Always try to swallow before you kiss. Moist, not wet.
Variation is everything, for instance suck and nibble the lips in between the tongue-probing.
Get your hands in on the action. Caress his face, hold his neck and pull him to you.
Every now and then, detour away from the lips, elsewhere on the face.
Don't dominate the kisses. You are kissing together.
Stop in time. Make him want to come back for more.