I always clean the block and sump mating surfaces, put some sealant on the pump joins etc then smear grease along the block mating surface, that way when you put the gasket on it sticks to the block and all you have to do is put the sump on

Make sure you put the sump in place real quick because after about a minute the grease loses its stickyness and the gasket will start to come off

Ive used this method for both the one piece and four piece gaskets and never had any leaks