I realize this thread is a bit stale, but in case the original posters looks back...or someone is considering enrolment in the art of sucking cock, I will add my two cents.
A lot of good advice in this thread. As has been said in a number of posts, don't give up after one try. But perhaps the best advice was the post that simply said, "I like to suck cock..."
A guy told me once, "the world is full of cocksuckers (he meant men) who don't know they are cocksuckers." They don't know, because they haven't tried. I was in my forties before I ever considered sucking a cock. I was willingly hustled in a coffee shop my first time. It was a disaster, but I knew one thing. I loved to have a man's cock in my mouth. I loved kneeling in front of another man and seeing his cock two inches from my face. I love playing with his cock and balls.
The last thing I will add is that every guy is different. If a guy is just getting a BJ and he would be just as happy jerking himself off; it's probably not going to be that great for you. But when you find a guy who loves to give have his cock worshipped and thinks that it is the duty of the cocksucker to service his cock--then, you will have fun. You will become addicted.