I have never French kissed in my life and when this guy french kissed my I didn't know what to do and I ran my tongue up under his. I really don't think that is what your suppose to do. Would that turn him off and never want to go out with me again? How do each partner french kiss? Do you take turns rubbing tongues?
Honestly, I have found that girls are the ones that are more worried about kissing than guys; I hear my female friends talking about if a guy was a great kisser or not...I don't think I have ever heard my male friends complaining how a girl kisses. I can't speak for all the guys, but as far as I'm concerned, sure kissing can be a turn on sometimes, but it doesn't matter much for me if the girl is a good kisser or not. Of course, I have had some girls that just nibble my lips and didn't know what to do with their tongues, so I would say, 'i guess you don't like tongue contact', and then they got the hint, but I think I was more worried about how long I was going to last! Also, I have had girls tell me, 'oh, I'm not the best kisser', then I tell her, 'then let's practice..' so if you're worried about it, just tell him that you don't feel confident kissing...no big deal.
Well, to be honest, if the guy you're kissing is going to make fun of you for your lack of 'experience', then he's not worth your time. Kissing is an emotional commitment, so don't go after it with just anybody.
Take a look at some of the other questions regarding french kissing for a decent idea of how it's done - I'm no expert, just self- and girlfriend-taught, so I'll leave that to the seasoned veterans.
If you're really that concerned about it, you can have a 'practice session' where you just teach each other what you like and maybe experiment some. It can be fun and you definitely learn a lot about each other.
Just don't feel pressured into anything, and definitely make sure he's a quality guy - french kissing is the 'gateway drug' of the sex world.