As well as the ABC and IDEAS principles of belays you also need to be aware that are are some other areas when rigging top ropes, where things can either damage you equipment or the rock. What we need to do is arrange some form of edge protection as in either case we want to avoid damaging the rope or the rock.
You can prevent some damage to the rope or the rock by using edge protectors. Some people use simple off cuts of carpet or doormats which they tie to the ropes that make over the belay. Other people use specific rope protectors. At a push when confronted with a sharp edge you can use a jumper or a rucksack to do the same thing, as what would you prefer a damaged jumper or a cut rope?