The first thing is to know him. Don't try it on a stranger. And don't try and like I did, no alcohol. Use every tool you can - except harassing him.
Do not just rush things Fond out what turns him on? How open is he to experimentation? Do you have a specific target in mind? Or do you want a general guide?
If you have a specific guy, find out what he likes, and be careful. Lead up to it. But don't make it public. Invite him to hangout either alone, or with a few other friends that you somehow convince to leave early.
If you are using the group strategy, it's easy - start it out with some games, some talking, then play some sex games.
Truth or Dare might seem immature, but with the right questions and dares, you can get far. If you do T or D you can get a wing-man involved and rig the game, but there is too much planning involved and I don't find it as fun.
Use a whole range of activities and conversations to loosen your target up. Talk to him, get everyone to open up and maybe get someone to show some skin.
Build a mood of relaxation, excitement and warmth. Keep him comfortable. Slowly, you need to arouse him - by this point he's probably already horny, but you need to make him really curious about you, and make it known that you are curious about him.
If you want use porn. Jerk off with someone else, or in front of him. Then make your offer.
It shouldn't take much persuasion, but you have to do it right. dont say "can i suck your dick?"
Try something more subtle, like if you guys are jerking, tell him you want to try something new. When I do this, the guys nods and moans. Give him a secretive smile.
If not, then you can
A) Make your offer, and hope he accepts. Be ready to defend your point.
B) If he is horny, just go for it. Move in on him, take off his pants, and just suck him off right there.
C) If you both feel high, make him want you to do it, be slightly provocative, act enticing, then go all in