The round-off flip-flop back tuck is usually the first airborne backwards tumbling pass a gymnast learns. It also stands as a basic building block for harder skills such as layouts, twisting, and double backs.

 First, before a gymnast can begin working on back tucks, he or she must be able to master the round-off flip-flop. Even more preferable is a fast and solid round-off to 2 flip-flops. This is important because the back tuck requires speed, power, and good body position. (Tips focusing on the round-off flip-flop can be found in the Back Power Tumbling article.)

 Once that's been mastered, now you're ready to begin work building towards the back tuck. Because this is a fairly big step up from back handsprings, you should follow the drills and steps that your coach gives you. This can be very dangerous if you don't have supervision. And because of that, I will only state a few key preps and drills.

 At this point, you should be comfortable with connecting two or more back handsprings to your round-off, and you should be able to finish the series in a good, tight punch straight up. In fact, that is the first drill. Do a round-off, one or two flip-flops, and punch as tightly as you can. Be careful though. If you don't have control on your punch, you may continue to fly backwards. Be sure to have a spotter.

 Next, lie on your back on the floor. Begin this drill by squeezing your body tight, with your arms by your ears. Then quickly, without using your upper body for leverage, tuck your knees and throw your legs over your head so that you automatically do a backward roll. The thing to concentrate on here is lifting your hips. This is what will give you the rotation to get around. Tucking your knees to your chest will do little for the rotation so be sure to know the feeling of lifting your hips.

 If you are having problems with this last drill, such as not getting enough speed to roll around, it might mean that your stomach muscles are not strong enough. In addition to this drill, be sure to do some extra abdominal conditioning.

 Back tucks should travel backwards. Ideally, you should come out of your back handspring in a hollow body position. Now, if you were to tuck while still in this hollow position, you would either greatly undercut the back tuck, or you will not rotate. So, you must get your body to continue traveling backwards. You have lots of momentum coming from your round-off flip-flop, and according to inertia, your body will still want to continue traveling in that direction. Normally, if you were doing another flip-flop, you would stick your feet in front of you to maximize that backward momentum, right? Unfortunately if you were to do this into a back tuck, you would keep flying backwards and get very little height. But you don't want to go straight up either. So, this is where you need to snap your upper body from the hollow position to an open-shoulder, open-hip position. You might want to think of this as a slight arch, but it is very slight. You still want to maintain a tight alignment. 

Do these drills frequently. You want your body to remember each of these movements so well that it becomes automatic. It will take time, lots of practice, lots of drills, and definitely a lot of tries. Good luck!