A blowjob can be a great experience for both me (the giver) and you (the receiver) but there are some do's and don'ts when it comes to the ultimate kiss. I gave a guy a bj just the other day and he definately had some mixed-up expectations and poor training when a girl goes down.
1. Don't grab my head: There is a big difference between pounding my pussy and pounding my mouth. My pussy doesn't have a gag reflex. I've seen vidoes where the girl is able to take an 8" dick all the way down her throat, but that is the exception, not the norm. So until you know the depths of her throat, I would advise you to just relax and enjoy and keep your hands off.
2. Cum in the mouth: This is a sticky subject (pun intended). I have some girlfriends that don't mind swallowing and others that do. I fall into the latter. One girlfriend told me that once a guy came in her mouth without warning and she threw-up all over his lap. Buyer beware!
So how do you know her preferences? Of course it would be an awkward moment at dinner if you ask "Do you swallow?" Maybe she does, but I doubt you'll ever find out first hand. My advice is when faced with this dilemma just let her know that you're cumming. Most of the time we can tell anyway (your body stiffens, the head of your dick swells, and you stop breathing), but be a gentleman and let us know. Now the ball is in our court. We'll either take it or send it elsewhere.
3. Enjoy the moment: Just like keeping your hands off my head, keep your hands to yourself. I don't need my nipples, pussy, or asshole played with while I suck you. My pleasure comes from what my mouth and tongue is doing to your cock. I swear, the next guy I blow is going to have his hands tied behind his back.
4. Return the favor: Most women I know like to have their pussies licked so after you're done, it's my turn.