you should also ask him, if you are doing it right to him, so in a way you will have a feedback on how well you do it to him.
guys like it deep throat, and based on my experience they really don't want when your teeth hits their penis.
do some variations like just licking him slow, then gradually making it fast. it is also additional stimulation when you include licking his balls, but be sure to be careful with that spot, it hurts when you hit it wrong.
just practice it with your bf and you'll get it right!
be sure that after you did it to him, make him return the favor to you! got it?

go girl!