Working Relationships
During your meetings, which should be a fair exchange between the party contracting and the prospective contractor, gauge your feelings and impressions you have about the person/organization you would be dealing with. Do they seem reputable ad reliable? Is this a representative or salesperson of the company and if so, who will be onsite handling the project? Know before signing. And be wary of attempts that get you to sign right now. Higher involvement decisions by nature require more time.

Does the person strike you as being knowledgeable and not just versed on the subject? Given the setting and your own set of circumstances/nature of the work, were appropriate product samples available or at least made reference to?

Experience
How many years have they been in the business? [Which also raises the question of financial stability and ability to stand behind a warranty].

How closely does their experience and track record related to your own project?

Have they been diverse in the sense that they'll be able to cope with an hidden unforeseeable that may rear, and fairly at that?

References
Look at your initial mode of contact. If they do or don't come by way of reference from associates, friends, or from those already in the business.

Still do your part. Become clear on the issues of cleanliness, professionalism and regard for the project overall from inception to beyond completion? Do their projects come in on budget and on time. Or within the timetable relied on for larger scale projects?

Does the company utilize subcontractors versus employees. [for the project receiver, the subcontractor arrangement can have disadvantages such as delays in completion, quality of work issues, and not as much influence over the finished product while employee-roles offer greater consistency as a whole. But this is no universal rule by any wild stretch.]

* Obtain at total of at least three references in any case.

Check with your local Better Business Bureau for registered complaints and current status of these, company history, and whether any outstanding issues have been resolved.

Cost
While the low bidder is favorable to many, and is usually most often chosen, consider what you may be paying for in trade for the lesser price; if at all. Are quality of materials possibly being sacrificed?

Also along with costs, you'll want to consider the payment arrangements. Specifically the percentage of retention or holdback - the amount withheld until completion, which is factored as an allocation to finish your project in the event the chosen contractor does not complete satisfactorily.

Licensing
Requirements vary from state to state. Check with your state department of regulation or licensing board or, county building department to get a grasp on..

Also don't take on good faith that the license won't expire during your said project so confirm expiration dates too.

Guarantee
Have specified any product/labor offered and for what duration. What exactly does the guarantee cover? All labor and material or will labor be separated out at that future date, only be stood behind by itself, as is so common. What circumstances and exceptions might apply to the proposed guarantee and is this guarantee in writing or only by word-of-mouth? Always this is an area that deserves extra attention and clarification.

Lastly, make sure any applicable code requirements are adhered to and which one of you will handle the needed permits, such as filing for and later sign-off with the inspector.

Here are some links to places that market the services of contractors.