I've been working on the problem for fifty years on the same creek in Cornwall. It is not just a kid's pastime.
1) Stone selection is vital. A bit of slate is good, but it needs to have some weight in order to give it "legs". Heavier stuff works better for me.
2) Back-spin and low delivery are vital
3) Mirror smooth water is essential
4) A couple of stiff G&Ts before addressing yourself to the task, as the darkness falls, tends to work. This is a mad sport where you are entirely unlikely to be hauled in for a drugs test. Your family may, however, call you in for supper.
Magic!
Good luck.