Practice, Practice, Practice
You should do some homework before you try to deep-throat a real live cock. I don't like to get into technical discussions about anything as pleasurable and emotional as sex, however, I don't want you to run into any unpleasant surprises that will turn you off before you experience the pleasures of deep-throating. You'll need to learn some simple details that'll help you overcome your gag reflex and control your breathing before the pleasures of deep-throating can really be enjoyed. Probably one of the first things you encountered when you started sucking his cock was a gag reflex when it went too far in. It's the natural tendency of your body to gag when a foreign object, such as a deeply thrusting cock, is sliding down into your throat. With practice you can learn to control your gag reflex. The next thing to learn is how to relax your tongue so you can slide his cock past it and down into your throat. You also have to learn to control your tongue during the entire time you're deep-throating. There's really not much learning involved. You've already gotten used to having his cock in your mouth, now all you have to do is get used to having it in your throat. Get a soft, flexible dildo of the proper size so you can practice with it in private at your leisure, the solid jellies are the most comfortable. Get what's called a "double dong" so that you'll have something straight with enough length to hold on to, one and a quarter inches in diameter and ten inches long is a good size to start with.