NEW YORK ( TheStreet) -- With the latest figures showing the housing market getting healthier by the month, it's time for those who have thought about selling to get off the fence and prepare for the spring, the best time of year to sell. Nationally, the average home sold for 8.3% more in December than a year earlier, the largest gain since May 2006, according to a report Tuesday by CoreLogic ( CLGX), the housing-data firm. December was the 10th straight month of home price gains, and prices went up in all but four states - Delaware, Illinois, New Jersey and Pennsylvania. CoreLogic said early data indicate that gains nationwide continued in January. "We are heading into 2013 with home prices on the rebound," says Anand Nallathambi, CoreLogic's president and CEO. "All signals point to a continued improvement in the fundamentals underpinning the U.S. housing market recovery." Of course, many homeowners are still in trouble and unable to sell because they owe more on their mortgages than their homes are worth. But more are moving into the black every month, and homeowners who are able to sell may feel recent gains are enough to get them off the sidelines. With a month or two before the spring market gathers steam, what can a seller do to get ready? Start by finding out just how much you will need to pay off your current mortgage. Ask the lender, because that figure may be slightly different from the one you see on the annual statement that should be arriving around now. Start interviewing real estate agents, looking for one who works full time and has been in business long enough to have experienced both the ups and downs. Also, use sites such as Zillow.com, Trulia.com and Realtor.com to assess current prices and estimate what your home might fetch. If the home is worth less than you owe and you want to sell anyway, start figuring how you can come up with the difference. If you must sell investments, for example, use this time to pick a moment when prices are up, and to figure which holdings should go first. That list would start with ones you don't expect to produce good returns. Don't forget that you may have to sell enough to leave some cash aside for taxes on investment gains. Make sure there are no legal issues such as contractor's liens that could get in the way of a sale. And if you will be buying as well as selling, check your credit rating to make sure your credit history is accurate. Start clearing out junk and tidying up, and get a jump on needed repairs. All appliances should work, doors and windows should open and close properly and light fixtures should function. As a rule, cosmetic improvements such as painting and landscaping are good investments for a sale, but it generally does not pay to remodel the kitchen or bath, since most major improvements cost more than they add to the sales price. Finally, avoid getting overeager. Home price gains have been gathering steam and most experts think they will continue. If you don't have a compelling reason to sell this spring, such as a new job, waiting may well be rewarded with a higher sales price some months down the road. Keep in mind that the next home you'll buy may be going up in price as well.