It's great fun. Tough, but good and improves a hedge no end. Instructors kept telling us to make the cuts deeper, so the bit that's left is very flexible rather than taking less wood out and having to force the stem over so hard.
We were told to make sure the resulting cuts and their bendswere smooth and sloping so rain water flows off and not collect in the cuts and rot the wood, like when youre pruning anything really. However, I have since seen several hedges which looked like the stems were half sawn through, then pushed over, leaving the cut bit sticking up and splinters around the bend sticking up to collect water! But, two years on, these hedges have grown and look fine.
Hawthorn and black thorn are incredibly resilient, so my advice is to go at it and not too worry too much about getting each individual stem and cut textbook. Starting is tricky... Good luck.