Don't worry, it'll come naturally. If he's not hard, just put your mouth on it and feel it warm and swell. If he is hard, lick it first- head and shaft - both to see what it tastes like and to wet it for when you take it into your mouth. Don't forget to lick and suck his balls too - for some guys that's even better.
I read in a pussy-licking thread on here that you should try painting the alphabet with the tip of your tongue on a woman's clit. That sounds like good advice for licking a glans! But it's also about getting a big satisfying mouthfull of cock, as far back as is comfortable.
Cum tastes weird, like nothing else, and varies from man to man. But there's no fresher nourishment available to an adult, unless you got a lactating wife, lol!
Health-wise, obviously make sure it looks healthy - no open sores! HIV-wise, main danger is taking pre-cum or spunk in your mouth if you have gum disease or a recent scratch. A good tip is not to abraid your mouth with a toothbrush beforehand - use a mouthwash if you want fresh breath. There's no additional risk from swallowing unless you've got inflamation of the throat. The stomach acids kill everything except a few specialised parasites.
But don't get any spunk in your eyes, it really stings!
Oh, and some guys just can't cum in a mouth and need to jerk off to climax - that's no reflection on you. Just enjoy yourself. And let us know how it went. | 
