Make sure that first of all you have a connection to him. If you know him well and he knows you well, things can flow more naturally.
If he lets you handle his rod, make sure to act calmly. Go slow and soft, rub it, massage it, hold it, flop it around and if he likes it, continue.
You can start kissing his penis, sniffinf it, licking it gently all around and make your way to his glans. Give careful attention to his tip and continue to go slowly and softly, watching him to see if he's antsy or annoyed, if so, stop and do something else with him that he's okay with.
If things are going well, you can slowly begin shoving his tip into your mouth, make sure you open your mouth well and continue to help him with your hands. Eventually he'll begin dripping his precum and you can enjoy that if you like it. Be careful as he'll begin to thrust at times due to the stimulation.
Just make sure to be watchful if you get him close to orgasm as he'll flare up and you don't want to injure yourself nor him so let him off and continue to squeeze and massage his tip, ideally after licking or spitting on your hands, and if you get him to cum, make his shots land on your mouth.
Hope this helps!