4 tips:
1. Make sure that he has washed recently. This is your first time and you don't want to be turned off by taste or smell.
2. Communicate. Ask how he likes it and suck on his finger first to see how far you gan go without gagging. Make sure that he knows as well so he doesn't try to force it farther.
3. Remeber that there is more than just the head. Don't try any fancy things at first, just smooth up and down with a tight seal and no teeth. Use your hand at the base and slowly go up and down with a slight twisting motion. Let him tell you how it feels.
4. The most important: decide before hand how to end:
- pull out and cum onto your chest, a towel or something comparible.
- let him cum in your mouth, hold it, then spit into toilet.
- let him cum in your mouth, and swallow.
If you let him cum in your mouth, make sure that you keep your mouth completely over it for at least 10 secs after you taste the first blast to ensure that you get it all. Not more than 15 sec because it will become too sensitive. Also have him warn you right before so you are not startled when he cums.
Also, if you taste the pre-cum and it is too harsh, stop and let him know that you have changed your mind and you will not let him cum in your mouth.
The ejaculate is not harmful by itself, but be careful about posible stds. Make sure that he is clean, or if not, use a flavored condom.