DO:

• Get specifics of the job in writing. A Few Tips on Home Improvement Contracts.
   
• Make sure the contractor is licensed. In Maryland, it is a criminal offense to do home improvements without a license.
  
  In addition, the Maryland Guaranty Fund protects you only if you use a licensed contractor. Check for an active license at the Maryland Department of Labor, Licensing and Regulation

• Also check for a trade license. 21 occupations and professions, such as electrical or plumbing, are covered by the Maryland Occupational & Professional Licensing Boards
• Lead Paint. If the contractor is removing or covering lead paint, see if the contractor is accredited to do this work. 
• Check for customer complaints - Call 410-230-6309 or 1-888-218-5925. Ask if complaints have been filed against a contractor and whether they have been resolved or are still open.
• Decide how any disputes will be handled. Before job begins, have contractor agree in writing to a some way to resolve a problem that does not involve immediately filing a lawsuit. Your Options in Resolving a Dispute with a Contractor.
• Put job changes in writing. 10 Tips on Dealing with Contractors.
• Inspect the job regularly to see the progress. During the work, make sure that both you and the contractor follow the plan set out in the contract.

• Forget to put it in writing. Do not agree to any job without putting it in writing.
• Be afraid to question. Do not accept any terms or proposals you don't completely understand.
• Pay 100% in advance. The Home Improvement Commission recommends that you do not pay more than 30% of the entire costs before the job starts.
• Immediately hire another contractor to fix any problems or defects. First, contact the original contractor you hired. It is best to list all of the problems you have with the job in writing, give the contractor a copy, and talk to him, if you can. Always keep a copy of any paper you give to the contractor.
• File a lawsuit against a contractor before you exploring other ways to solve the problem, such as mediation. Review your options in resolving a dispute with a contractor.