I have a sort of side interest in economy, and this is a subject that gets a lot of coverage in it.
What you must NOT do is reward the wrong sort of behavior. So for instance if you give them a bonus on how many houses they do you might find that they lean more to quantity than quality. I have often wondered if tales of "I had a bill for my windows to be cleaned but they never did them!" stem from these types of bonus's.
My own personal favorite is the costco bonus. The guy who founded it is a bit of a genius anyway but his bonus structure is gob smackingly simple.
What he does is increase the wages after a 90 day probationary period then every 800 hours worked until they reach a ceiling. This means he can be picky about who he employs as generally they tend to stick around. He can demand a lot of his staff due to the fact that even a shelf filler is actually a career with wage increases rather than a job.
Think back to some of the jobs you have done, how many of them would you still be doing if you had the incentive to get up and work towards your next pay increase, and the one after that, and so on.