Yeah there's not a lot of advice to give on back tucks. They're such a technically simple move. It's just courage and commitment. Jump as high as you can, and when you get there, tuck.
On foot - For a perfect back tuck keep looking forwards. Push your pelvis forwards and let your shoulders start the rotation instead of whipping your head back and arching your back. Whipping and arching seems easier at first, but it will never look as clean or get you as much height as looking forwards. Remember, jump up. Not back.
I learnt them on grass and bark. It took me about 2 hours. On bocks I would definitely recommend finding a gym with fellow bockers to throw crash mats in. I'm not confident with them yet since its a new trick for me. I can only do it with a crash mat... and not always then! lol. I don't seem to be able to do it with the technique described above either... I need an initial whip to start the rotation, then I tuck. ...But I imagine once you're good at them it's the same as a flip without bocks. (Is that right? - people who are good at them?)
