'Cause it's a topic of conversation--this is something I wrote a while ago. It's quite detailed.
Tips from a Fellatrix
The first thing should be obvious, but is overlooked by many women.... Love what you do. The more into it you are, the more they will enjoy having you do it. Too many women are apologetic or hesitant about giving head. (Dunno about men, the male cocksuckers I know are generally enthusiastic.)
The Approach: you don't have to go straight to the cock. Kiss his chest, his belly. Open his thighs and kiss inside them, kiss the crevasse where legs meet hips. Brush his balls and his cock gently with your face. Kiss the pelvis on either side of it. A fun way to take him in your mouth at first (works best if he's lying down, as do most of these techniques) is to lean over the head, and press your lips to it, and pull him in with a little suck - not using your hands. Or hold him up and tease it with your tongue a moment.
Lubrication: If you press your tongue to the roof of your mouth slightly, it can help activate the salivary glands. If you have a tongue ring, the pressure from this can help. Also, just think about getting your mouth around that yummy cock. Then, when you approach it, let the saliva drip onto it, and push the saliva over it with your lips. Messy is good. The more the better. You can even play with just doing this. Backing off, letting the spit gather in your mouth, and then spreading it with your lips. This can be alternated with any of the other techniques - but I have found that it's nearly impossible to use too much. Most men love the feeling of spit dripping down their balls.
Suction: You can't suck too hard. Really, you can't. It might seem like if you suck that hard, you're going to pop a vein - but go ahead and try. Learn to form a suction with your mouth. You can practice this without anything in it. Pull your cheeks in without using the muscles in your face. Just suck. Like you are drinking a milkshake that's too thick. The tongue drops to the bottom of the mouth and pulls slightly back. Feel that? You can use that. (more on the tongue later). When you are giving head, do the same thing you do with your pussy - relax as you take it deeper, then tighten as you pull back. Open and down, then suck and up. If you pull back as far as the head, this may cause a popping sound as the shape causes the suction to break. You can even do just that, take a teeny bit more than the head, and suck hard while bobbing, breaking the suction as you slip back across the mushroom each time. This reminds me -
Noises: Wet, sloppy, slurping, popping sounds are a good thing. You will find when you get into it you are making all kinds of noises you don't hear other women make when they are giving head. Forget that - look at the man you are sucking. See - he loves it. Also - try humming. A little vibratory hum as you bob your head (can't really do this while sucking hard), so that it tickles your lips a bit, can be fun. It's a male vibrator.
Tongue: This is our secret weapon. They can't see what you're doing with it, but they sure can feel it. As you start to go down, hold just a little more than the head in your mouth, and flick your tongue across it. Swirl it around it. Press it into the opening slightly. Move slowly and take more in your mouth, and as you do, press into the vein on the underside of the cock with your tongue, running it along. You can use the tip of the tongue for firmer pressure, or the flat for broader. This is where a tongue ring is most useful - you can get both sensations going. Flick the tongue up and down as you hold him in your mouth. Stroke and rub it. Open your mouth wide and circle him with just your tongue. If you can take him all the way in your mouth, a little rolling movement at the base of the shaft is good.
Hands: use them. While there are a few men who prefer you not to use your hands, most will appreciate it if you do. Wrap one below your mouth, and move it in unison with your head, effectively extending your mouth. Use two fingers or the whole hand. If you need to pull off a moment to relax or gasp for air, keep your hand on him. Never lose contact. You can also use your fingers like a cock ring, holding tightly at the base. Or move in opposite to your head movements. Your other hand can be cupping his balls, which brings me to...
Balls: Don't neglect them. Give them some love, too. Keep them cupped and supported. Rub your thumb in the center, pressing into the base of the shaft and down across the balls. Roll them across your hands. Even depart from the cock a while and take them in your mouth. Lick them, and then suck them right into your mouth, rolling them across your tongue. (Remember to keep a hand on the cock while you do this.)
Prostate: reach under the balls and find the line like a tension wire there... run your fingers along it. Do this while you are sucking and bobbing on his cock. There may be a small indentation. Press into it with your finger, gently at first, then harder. Massage this area. If he'll let you penetrate him, you can get a better angle (and easier to maintain position) by sticking a finger an inch or so into his anus. Then press back upward, toward yourself. (Crook the finger in a "come here" sign.) Press on and massage this area. It's ideal is you can do this as he is close to climax, as the additional pressure will make him cum harder. Sometimes it will cause him to squirt a decent amount of pre-cum, too.
Movement: Most men like steady, rhythmic movement. Take a little while playing and varying technique, but spend most of your time just bobbing your head at a steady pace. It's better to have a steady pace than to try to go too fast and need to stop. When he gets close to cumming (you will feel the tension in his muscles increase, and the vein pulse a bit - some men stay at this point a long time, some only a moment), then you can speed up and go fast. You can vary the movement from simple up and down (with varying degrees of suction and various tongue movements), to a kind of circular motion. Just move your head in circles as you go up and down. Or a figure eight, which is cool if you have him deep, and you press your nose into his pubic hair (or bone) while you do it.
RELAX! The biggest problem for most cocksuckers, and the one that will keep them from being able to go long or enjoy it, or to deep throat is tension. Relax your facial muscles, esp. your jaw, and your shoulders.
Deep Throat or Face Fucking: see above - the key is relaxation. For all other techniques, you do try to keep some tension in your mouth. If you are having your face fucked, or you are trying to deep throat - don't. Relax completely. You may gag a little, and that's ok - just relax afterward. When a guy is about to cum, I like to take him as deep as I can. The more turned on I am, the deeper I seem to be able to go. I just open up my throat like I'm yawning. (Try yawning with your lips closed and you'll feel what I mean.) I like to have him pressed to the back of my throat while he cums.
Tears: A lot of women tell me they can't give a decent blowjob because it makes them tear up. Well, me too. I just don't let it stop me. Hell, a lot of men find it incredibly sexy to see those tears roll down your cheeks. This is strenuous work. Don't try to pretend it's not. Most men will be flattered that you are willing to work so hard for his pleasure.
finally - the Orgasm: I've mentioned that you can feel the tension increase before he cums. This is a good time to stimulate the prostate, and to speed up movement. You can also go deep and hold it, but the timing has to be more precise, because if you stop moving too soon, he may lose the orgasm and have to be brought back to it. After he cums, suck hard, and pull up on his cock slowly, firmly pressing your tongue to the underside. Suck every bit of cum out. Circle him with your fingers and pull up behind your lips. Sit back and watch yourself squeeze that last drop of cum out onto his head, and give it a lick. Oh, and if you don't want to swallow - remember what I said about not losing contact. Keep a hand there, not so tight... and then tighten it and pull up to squeeze out the last of the cum.
Individual preferences vary, and the most important thing is communication. It can be verbal, or it can be just paying attention to your partner's body language and responding. It's all about paying intense attention to the cock, and the man attached to it, in front of you.