You need one thing to play rugby, and that is to be able to enjoy physicality. Rugby is not a dangerous sport.. it has less serious injuries in general than other non-contact sports.
You need to learn how to take the ball into contact without injuring yourself and the opponent, whilst getting maximum gain and setting-up an organised ruck. Players only get injured when players have malicious intent, rather than the actual ruck itself.
I find that if you charge with your shoulder as you go into contact as low as possible it helps as you go to ground. When you are on the ground, release the ball the best timing you can and then cover your head with your hands, sort of like a brace position on your side, with your legs together.
I found that it helps, as there is less to get trod on. The only time i got injured in a ruck was when i was getting punched in the mouth, bitten, pinched, scratched etc by cheating assholes. It's not the actual ruck, and it's not every team who uses that cheap ass tactic.