I have been in the business of sucking dick for 14 years. That makes me feel whorish, but whatever.
Good tips: 1) I learned this one from Jenna Jameson: Chew gum ahead of time. That is so that your jaw muscle won't get tired since some guys take a long time to cum. 2) Lick the underside of the dick around the tip. That is the most sensitive part. 3) Alternate between going all the way down, and just licking the tip. 4) And vary in rhythm between going fast and going slow. 5) You can tell when a guy is going to cum because his thigh muscles tense up. BE PREPARED! If you want to let him cum in your mouth, don't stop. But if you don't, start jacking him off. It will save you getting pissed that he came in your mouth.