Check references. If possible, view earlier jobs the contractor completed.
Check with the local Chamber of Commerce or Better Business Bureau for complaints.
Be sure the contract states exactly what is to be done and how change orders will be handled.
Make as small of a down payment as possible so you won't lose a lot if the contractor fails to complete the job.
Be sure that the contractor has the necessary permits, licenses, and insurance.
Check that the contract states when the work will be completed and what recourse you have if it isn't. Also, remember that in many instances you can cancel a contract within three business days of signing it.
Ask if the contractor's workers will do the entire job or whether sub-contractors will be involved too.
Get the contractor to indemnify you if work does not meet any local building codes or regulations.
Be sure that the contract specifies the contractor will clean up after the job and be responsible for any damage.
Guarantee that the materials that will be used meet your specifications.
Don't make the final payment until you're satisfied with the work.