Alright so yeah I remember my first kiss I was freaking out beforehand! In fact I asked a question just like this one ha ha and most of the answers said things like "go with the flow" and "let it happen naturally" and I was disappointed because i thought there must be more to it!
Then when it finally happened, it did come naturally! It's hard to understand before it actually happens, but it;s as though your body already knows what to do
But, I wold say don't wear lip gloss- it'll be sticky, could smear off your lips, and be awkward for the guy if it's on his. Try using chap stick! Or, if in a pinch, lick them right before the kiss just to make sure that they're moist.
If you are sitting down, lean towards him with your shoulder and slip your arms around his neck. Thats what I usually do, rest your elbows on his shoulders and you can gently cradle his head as though it's a head-hug (sounds kinda strange but it's pretty natural)
OR
you can bring your arms around his waist
My number one tip would just be to follow his lead. Don't initiate anything (like using tongue) unless he does first!
Have fun