This is the most popular type of kiss. This involves touching your tongue with your partner's and it can be quite a pleasant experience. There are a few tips to create a great French kiss.
You lips should be relaxed, you body should be relaxed, otherwise it will be like kissing a dead fish for the other person. There are only two things involved in a French kiss: your lips and your tongue. That's it!
Your lips should be slightly parted, not open wide like you're at the dentist. Open them just far enough, just like you are regularly breathing through your mouth.
Do not have your face dead on to his/hers, otherwise your noses will touch. You want to move your head to one side just enough so your nose is out of the way of theirs. If you think about it then, with your head tilted one way and his the other way, your mouths will not reach dead on. Your mouths will meet at the corner of the other's mouth. It will look like the picture below.
If you look closely at the picture, you will see that their noses will actually touch the cheek of the other person. Their lips have already touched. When you touch the other person's lips and you stretch your tongue out a bit, your mouths will instinctively open as much as the couple in the picture.
Practice on your own if you'd like. Open your mouth enough (while you're by yourself of course!) just enough to stick a bit of your tongue out. It will go past your teeth. Don't stick your entire tongue out... just an inch or two. That is how far you should stick your tongue out in a kiss. So your tongue will go into their mouth and theirs will go into yours. When this happens, both of your tongues will touch. Then just circle the tip of your tongue around the tip of theirs. If they do something different (because you have to remember that everyone kisses differently so some may move their tongue around a bit differently) then just do the same as they do. They may flick their tongue over yours and you can do the same. Or they explore the inside of your mouth with their tongue, do the same thing! Or you can just lightly touch their tongue while they are exploring. The best thing is to NOT just leave your tongue doing nothing.
As for movement of the head, that is entirely up to you. Some people will move their heads very slightly in a small circular motion or figure eight. Sometimes they won't. Sometimes just one person moves their head and the other doesn't. It's totally up to you.
You may explore different ways of using your tongue. Try running the tip of your tongue over your partner's lips. Do this slowly and gently, just using the tip of your tongue.