Expect a contract. A contractor should include the scope of work and a price. If your contractor doesn't provide one, make your own.

Does he have insurance? General liability and workmans comp is essential. Proof of insurance should be provided.

References. Look at a job or two. Most pleased customers won't mind recommending their contractor.

License. A contractor should be able to show you a copy of his business license

Warranties. Can he provide a written workmanship warranty of at least one year? Also watch for manufacturers warranty. You need paper in hand to ensure you are getting what you paid for.

Don't pay any contractor up front. This is generally bad policy. If the job is more than a contractor can finance, pay for materials when they are delivered. This way the materials will be at your home even if the contractor is not.

Who cleans up the debris? Yes, some contractors expect you to clean up after them!

Who will be doing the work? Will the contractor be doing the work or at the very least, oversee the work? Or will he be hiring the job out to someone else?

I certainly recommend that you get several estimates. And I don't expect to get every job. But I do want to give you a few words of caution about hiring a contractor. Before you entrust your home projects to the lowest bidder, check him out.