When you check references, ask if you can visit their homes and see the work the contractor has done, said Vince Wiscovitch of Manhattan-based contractor MyHome.

Before you hire, ask the contractor for proof that he has workers' compensation, disability and liability insurance. Otherwise, if anyone gets hurt during your renovation project, you're responsible.

Choose a contractor who's done lots of renovations in the type of building you live in, said Colleen Barry-Sleicher of Manhattan Home Improvement Referral, a search service that matches consumers with residential contractors. The work that needs to be done in renovating apartments built before World War II is different from that in more modern flats.

Once you pick your contractor, get a clearly written contract that itemizes all the work to be done, and the cost of materials and labor, said Beatrice Ortega, president of Dot Construction of N.Y., located in Morris Park in the Bronx.

Be sure the contract includes a "lien waiver" - it allows you to not make your final payment to the contractor until he has paid subcontractors and vendors. This will cut down on the chances of them putting liens on your home because your contractor hasn't paid them.

Also be sure the contract specifies that the contractor will buy the construction supplies and accept delivery of them - or else these will become your problem.

Ask the contractor to guarantee the price of the job, Wiscovitch said. The guarantee can say that the price will be X unless specific problems occur, in which case it will be higher. A smart contractor can figure out what problems would be likely to occur - and what a job will really cost if they don't.

Contractors who won't give a guarantee may be offering low-ball bids to get your business - and planning to jack up the price later, he said.

Demand a written warranty of at least a year's duration for the work that's to be done, Wiscovitch said.

Have the contractor write up a work schedule.

Don't pay more than the cost of materials as your deposit, Ortega said. Most of the bill should be paid only after the work is done, and you've okayed it.

If you live in a co-op, make sure your contractor meets with the board before construction starts. He needs to know what hours he is allowed to work in your building, what elevators he can use and where to store construction materials - and to obey these house rules, said James Ortega of Dot Construction.

Whether you live in a co-op or condo, see that your contractor cleans up areas where workers track dirt or make any other kind of mess.