A lot of companies ask for feedback once they've completed a job. That's important, but the bulk of what you hear back will be all the things you're doing right. If you want to know where you're going wrong, try surveying customers whose jobs you didn't get.
"I want feedback at every possible opportunity," says Ken Cowan, owner of Bridge Street Building & Design in Linden, Mich. "You can't overcommunicate with a potential client." So he sends these "lost job" surveys to all the clients that got away. He says he gets about half of them back, in part because he'll send a second one, if need be.