Honestly just relax, you can't really do anything wrong, just make sure you have fresh breath, look into his eyes and lean in.
Here's a couple of things I've found out through kissing:
-GO SLOW to start, you're less likely to feel clumsy and awkward if you start with soft gentle kisses
-USE YOUR HANDS not in the kiss directly obviously, but touch him(not his dick straight away). Start by resting your hand on the back of his neck/head, and if you get more into it gently tug on his hair(guys go wild). You could also rest a hand on his shoulder or thigh if it makes you more comfortable.
-SMILE at him when you pull apart and look into his eyes
Good luck, you will be fine xx
I'm always happy to help if you want to talk to me
Almost 16, and I like to kiss my boyfriend...a lot ;)