In gymnastics with cheer leading, a big stepping stone, for tumbling would be the round off back hand spring. This is, required by any cheer leading gym to be on a competitive team and is also a huge skill in gymnastics in order to get to higher level gymnastics. Some good drills would be, just learning how to continue your backwards motion out of a round off. So, after successfully learning a round off, you'd want to therefore round off up onto a mat, standing up tall and then drop backwards onto another mat continuing your backwards motion.
You don't want to force yourself into the back handspring. You don't want to force the jump backwards. You want it to happen naturally because that's where your momentum is going. Some other good drills would be to do a round off, over top of what we call a mailbox or some kind of sturdy object and work on jumping backwards. Round off jump backwards onto a mat stack, which is about hip height, landing throughout on your back. Again arms up tight, feet together, just initiating the jump back for the back handspring.
From there you would want to always get some mats out. You would want to go round off back handspring across some soft landings, some soft mats, in case there's any fall or you don't want to get injured. And then from there, on to the floor, round off back handspring with the spot. After you've achieved all that, and the coach has given you permission, you may do it on your own and successfully have a round off back handspring.