Inspect the work quality. Ask if the project came in on time, if the bid costs were close to the final cost, and if the contractor was easy to work with. Bids are important. Get at least three bids on your project. When the contractors look at the project, have in mind clearly what you want to do, but listen to their input.
Experienced contractors can often point out overlooked and unforeseen problems.
Weigh your options. Do not necessarily accept the lowest bid. Some contractors may bid the job low in hopes of increasing charges as they go. Others may bid it incorrectly and then cut corners on the job. Others may bid it right and still be low, which is what you want.