The best concept for giving head is MODERATION. Start with a touch, progress to a kiss, then lick slowly, then lick rapidly, wrap your lips around em, suck on em, pull on em wit ur lips, ultimate is gently gnawing with your teeth.
When done in this order, pay attention to your lover's response, does he seem to be enjoying it? Does he look like he's uncomfortable? Are his toes curling? When you get to the point that he appears dissatisfied or uncomfortable, STOP! You've reached his level of tolerance. This can be increased with him, but in each case, simply guage your behavior by his response. If he likes it, go a little further until he doesn't and that's his threshold. You can "break em in" and increase the threshold but only with patience and time. Once you've found how far you can go, use ur imagination but don't cross that line.
And ask!! Guys will NOT hesitate to tell you what they want, any hooker can tell you that.
*RULE #1 OF GIVING HEAD!!!*
Adjust your attitude. Whether you enjoy giving head or not is 99% irrelevant. I get pleasure out of giving head, but its an act more directed towards the recipient. DO NOT make him feel like his penis is some gross monster. Your attitude can enhance OR ruin the mood. If you choose to give head, make it look like you're enjoying it. Make him feel like you need and want to do what you're doing. If he looks down and sees that your face says "I'd rather be at the library than sucking this dick" you might offend him or hurt his feelings. Yes, guys DO have feelings. Guys are insecure about their guy parts. They OBSESS over their guy parts. The existence of LPSG proves that. If you work this hard to accomodate your lover, it will justify the same accomodation for yourself. I went down on you and blew your socks off, now it's my turn!! As I always say, suck that dick like there's gold in the middle!!