Great question... I've recieved plenty of these and can tell you I've got a pretty good idea on what's going on with em.
It's really 50% mental 50% physical. 1/2 the work is pretending it's the most awesome thing to ever happen to you at the moment. Guys love when women are heated up and into it. Nothing worse than a girl who shows hardly any emotion.
Not much to it really. What you've probably heard or seen in movies is about as straightforward as it gets.
The word sucking gets kicked around a lot, but there is really none involved. Obviously, you know you put your mouth on the dude, and just basically move your head back and forth.
That's just about it. There are little things you will learn with more experience. Like a favorite of pretty much every guy I know is when a girl goes deep to her gag reflex or beyond. That really is the "G-spot" for hummers.
Try experimenting. Don't just thrash your face around and try to blow him up, unless he' requesting that... Another good technique is to stick out your tongue while performing past your bottom lip. This allows you to feel more and control the sensations better.
But remember, it's 50% attitude. I love when a girl just moans, caresses it, rubs it on herself anywhere, etc. Your competing against millions of girls, so do some fantastic acting and have fun!