There are a couple different variances in roundoff technique just like with any other skill. The main principle no matter what the technique is to efficiently change athlete from using forward facing momentum to backward so they can go up or back depending on the desired angle of trajectory.
You’ll find the hurdle and lunge entry technique typically stays the same. We have all been taught to have a straight body line, strong deep lunge, with a big heel drive. The most underrated and under worked part of the roundoff in my opinion is the block. Strong block through the shoulders allows for better height and control of the ending portion of the roundoff.
Most of the time, your roundoff will go into a backwards skill (like a back handspring, or whip) the ending of that roundoff should over rotate so that we can get the feet in front for a more efficient punch into the back handspring . The ending of the roundoff and position of arms can vary depending on the skill that is being thrown after the roundoff. Always do your own research and find what works for you and your athletes.
Priority is to always make sure that you or your athletes are conditioned, and technically sound in basic tumbling movements, before progressing to harder skills.