OK, my biggest turn-on when getting a blowjob is something quite a few women will never manage to do: Deepthroat. For a good lesson in how I'd like it, watch Heather Brooke of IDeepThroat. Unless you don't want to pay for the advice, here goes:

Training first and foremost. I'd like it to go as smoothly as swallowing a glass of water. As I said, not all can do this.
When "your" mouth is at the root of my cock, it's nice to feel your tongue licking my balls. Again, something hard to accomplish as it adds to the regurgitation reflex.
A finger or maybe two up my ass massaging my prostate. Quite a few men don't want this.

Now, with the most difficult part taken care of:
Teeth. Not biting hard, but nibbling a bit. Slowly withdraw from the cock and let your teeth slowly draw along the shaft. Just open up slightly when you get to the rim of the head. Move your lower lip up so your lower teeth isn't at the base of the head, but tentatively scrape your teeth across the head. Don't do this too much though. It will get sore after a while.
Between the balls and the ass, there's a place (which, translated from Norwegian) is called "the fold". Medical term might be the perineum. Very sensitive area to a finger, a nail (lightly scratching it makes me wild) and licking, either with flat tongue or the tip of your tongue.
Using the tip of your tongue, lick around the base of the head, the most sensitive part of it, and also the line of flesh under the head.
What I haven't experienced yet, but makes me hard just thinking about it, is also from Heather Brooke: Let the first spray hit you on your face, in your hair, mouth, on your tits, wherever, then swallow/deepthroat that cock and let the rest go straight down.

Well, that's how I like to, or with some examples, would like to, get a blowjob. One thing above all that makes me love it even more is seeing my cum drip down the face of whoever I'm with. But that's a personal reference. Most of this is simply physiology though, knowledge gained by reading and testing.

I hope this has helped you ladies somewhat. Of course, any variation you might think of is fine. Even a bad blowjob is a good blowjob. Other places too might heighten the experience for the man. This is up to yourself and your courage off course.

Good luck.