Girls and guys habit when doing HJ?

don't stop until the cows come home, baby

Please give it until he cums. Whether you're giving a handjob or blowjob, keep it up until the guy cums because the best feeling is just before and while he's cumming. The head and that sensitive spot just under the head gets sooo super sensitive during that time, so that's the time to double your efforts and finish him off good and give him something to remember. However, if your right- handed (or left-handed) have some tissue ready to use with the other hand. Then when you know he's very close, take one or two tissue with that hand and while you give your last few strokes, just jerk him off in there. It would definitely not be a good idea to stop before he climaxes because then you'd be leaving that all up to him and wouldn't be a great idea at all. I don't think most guys would like that. Always finish whatever you start whether it's a hj or bj.

Don't stop! For guys climax is the goal. This is different from women.
Google 'good hand job' for instructions. I'm not making this up!

Ted

As the girl gets more experience giving a hj, she'll learn to time it such that she stops just at the moment of orgasm.

I agree with cun7n1nja, it's much more convenient to use your mouth to make them climax.

I would keep going until he's completely spent, because in my experience, guys have liked it when I 'milk it for all it's worth' and don't stop until the orgasm is really over. Or I'd just finish with my mouth and avoid the mess altogether, haha, but same idea.