Explore. Do what feels right. Make it fun, playful, romantic, whatever you want it to be. Don't make it all about jamming your tongue down his throat, and try not to drool all over him, because it's generally less than desireable to do so.
If you come off as confident it'll be a lot more fun. If all evening you're thinking "Oh my gosh, this is going to be bad" you won't enjoy yourself. Follow his lead at first, if you're truly that nervous.
And really, it's almost impossible to find a truly bad kisser. If anything, they might do something you're not used to; give it a chance before you hate it. Who knows, he might be thinking the same thing right now about you!
Over time, you'll develop your own personal style of kissing/making out, and that's not a bad thing. Do whatever feels good/right to you, and gets a positive reaction. For example, some people love a gentle, or less than gentle, bite of the lip, "necking", and other techniques. Like I already said, experiment & make it fun!
From personal experience I'd advise that you brush your teeth and floss, and have some mild mints with you, like TicTacs. Fruity is usually good, and less overpowering. If you're at a party, don't worry too much about what you're eating if you're both eating the same things, but a huge plate of hummus & extra garlic is a bad choice right before kissing =P. That's where mints come in handy for both of you. Casually offer him one if he's been gorging on something stinky.
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