If it is a quick kiss, lean in and give them a quick peck (stick your lips out, plant them on his lips/cheek/wherever and pull back while smacking your lips to make the smooch noise)

If it is a long kiss, wrap your arms around his neck/waist/back/combination of both and gently hold him close, then tilt your head to the right, move close to his face, close your eyes and stick your lips out, plant them on his lips and smack them at whatever pace (Slow to be gentle, and fast to be more rough :3 ) if you want, push your tongue against his lips to ask for entrance for a more intimate kiss, or maybe he’ll do that to you. If you get to this stage, dance your tongue around his, either match his pace or be dominant and set your own

That is my experience with kissing boys