By understanding your anatomy you will begin to understand the requirements that will allow you to take the full length of your mans hard cock into your mouth and all the way down your throat without choking you. The biggest obstacle is the fact that there is a bend of almost ninety degrees behind your tongue leading down into your throat. So the first thing you need to do is get his cock past that angle without you gasping for breath and ruining the moment.
In order to practice this, get in a position where you can tilt your head in such a way that your mouth and throat lie almost in a straight line. The best way to accomplish this position is to lie on your back on the bed with your head positioned just over the edge and tipped sharply back. This position will put your mouth and throat nearly in a line and will allow him to approach on his knees giving you full control over how much of his cock you can take. You can then gently guide him in and out of your mouth at your own pace by grasping his buttocks and pulling / pushing him. Keep a firm grip on his cock with your lips and keep your tongue as straight as possible.