I was worried about that too, before I’d kissed anyone. There’s not really anything you can do to prepare, because the way you should be kissing is really dependent on the way that your partner kisses. Just keep your lips in good condition (regular scrubs, regular lip balm application), and when it’s time for the kiss, keep your lips soft and relaxed, moisten them a little, and then just try to respond to what your partner’s doing.
It can be intimidating at first but it gets a lot easier once you understand what you’re actually supposed to be doing. And don’t forget to do something with your hands.