​The hardest part of any home renovation project isn’t the work itself, it’s finding a competent and reliable contractor to do the job. Painting, installing kitchen cabinets, knocking down a wall or retiling the bathroom is simple compared with the struggle of hiring a quality contractor who will perform at a high level from start to finish.
Everyone has heard stories about horrendous contractors who started a project and never returned or
projects that cost three times the contractor’s original estimate.
Expect
a contractor to be too busy to start right away. Some of the best contractors are the busy ones,
Ask
what work will be done by the contractor’s employees and what work will be done
by subcontractors. Make sure the contractor won’t be using casual labor hired off the street.
Sign
a detailed contract. Make sure your contract spells out exactly what will be done, including deadlines, payments options, the exact materials
that will be used down to the model number and who will provide which materials. “If you don’t have it documented, it’s your word against theirs,” Hicks says. If
the builder’s contract is not detailed enough, write up your own or provide addendums. Any change in the project, whether you change your mind about
products or ask for additional projects, should generate a written change order that includes the new work, materials and cost.
Choose
the right contractor for the right project. Someone who did a good job roofing your neighbor’s house, isn’t necessarily the right person to paint 
your home. You want to find a company that routinely does the kind of project you want done and not "jack of all trades, master of none". You also don’t want them to use you as a guinea pig.
Check 
complaints and litigation history. 
Check the disciplinary boards, Better Business Bureau and local court records for problems. Ask the contractor for a copy of his
license and copies of the licenses of the major subcontractors who will work on the job.
Check
references. Talk to both clients and subcontractors, who can tell you if the contractor pays them on time. “See if you can talk to current
customers,” because those clients have the most recent experience working with the contractor.
Read online reviews, but don’t consider that enough information! 
Yelp and Google also have some reviews. You want to read the reviews carefully (specially older reviews, because newer false reviews may mask the truth )to make sure the contractor is the right person for your job and will work well with you. Keep in mind that reading reviews is not a substitute for checking references.
Don’t pay more than 10 percent of the job total before the job
starts. You don’t want a contractor to use your money to finish someone else’s job or run off with your deposit.                                         (U.S. News)