being organized, have a game plan and dont stray from that plan, be prepared.
I usually walk through with a customer before I start so I know exactly what they are looking for and what rooms so I dont have to track them down a million times during an install.
When I have time, I premake many lengths of cat-5 jumpers and coax jumpers. In companies that install cable nids I have herd of having a ground block with a piece of ground wire hanging out of it and screws started in the box. Not really a secret I guess.