It depends on a number of factors, really.
If I'm really horny before I start, I'll sit or lay down, maybe look at some pics or a vid and jerk myself off fast and furious until I cum. Then a quick cleanup and back to doing whatever I was doing before. It's also good if you don't have a lot of time (before work, etc). Sometimes, it's not as satisfying so I have to jerk off again later.
Other times, I like to take my time. I'll put on a video or come to NN and pull my pants down long before I'm aroused. As the movie plays or as I browse through the profiles I'll get an erection then start rubbing and stroking it slowly. I love to take my time fondling myself look at all the various profiles here. If I feel myself get too close I'll try to back off and bring myself up to the edge again until I'm ready to cum, but if I'm looking at a particularly arousing picture I'll just keep going and cum anyway.
Also, when I cum after a slow one, I like to just around and totally come down from the orgasm before I pick up and move on. Usually this means I'm still sitting at the computer with my pants around my ankles long after I cum. If I hang around NN for too long after cumming, I'll start to feel the urge to go again. As long as I have the time, I'll let myself get aroused again and start the whole thing over. The second time can really feel great because you're already a bit drained from the first orgasm so when you cum again you really get wiped out.