You could try and build your confidence by practicing with a friend, if it would help you feel more confident, not sure if you would be at ease with that, I wouldn't be but I know other people who have, and it's just a though...
I think the key is not too stress. If you stress, then you will analyse what you are doing a lot more, and this will probs be reflected on the person to whom you are kissing.
My advice would just be to take a deep breath, relax and let things happen the way they are intended. As someone else said, everyone kisses differently. I would suggest that you make your tongue rub against your partners, maybe swirl it about a fewtimes and just see what happens - follow their lead, until you get your own technique.
You will be fine - just don't stress!