By Danny Teigman/The Star-LedgerFebruary 08, 2010, 8:00AM

As any frequent flier knows, racking up free airlines miles is easy. Cashing them in for a cheap winter ski trip or maybe a quick jaunt to Europe — well, that’s a different matter altogether.

Unless you love the tropics in mid-summer or have reason to travel to Akron, Ohio, any time of the year, turning those accumulated miles into free travel is getting tougher and tougher.

“The biggest pain in trying to use your miles is finding a set of days that you can actually go where you want to go,” said Chris Lopinto, president of ExpertFlyer.com, a website that tracks seat availability and fares. “All the airlines want to do is to get you to buy a ticket for the highest price.”

Travel experts say there are a couple of strategies that can help. the best bet is to be as flexible as possible about the day and time you are willing to travel. planning a trip months in advance and booking far ahead also help. Airlines add new flights to their schedules 11 months out, so the earlier you book the better.

Several websites also have sprung up to help travelers track down what seats and flights are available. and thanks to a change in accounting rules, airlines now have a greater incentive to get unused miles off their books, which could loosen things up a bit. If you’re looking for help, here are a couple of websites you might consider, some of which charge for their services:

• ExpertFlyer.com and MileageManager.com. Similar to Google alerts, both sites alert users to the latest deals that match their desired travel itinerary. ExpertFlyer tracks up to 28 airlines, including Delta, American. Alaska, Hawaiian and Air Canada, among others. MileageManager allows users to input up to five different travel plans on 10 airlines, such as American, British Airways and Continental. Both sites come with a price. after a free trial period, MileageManger is $14.95 a year and ExpertFlyer is $9.99 a month.

• StarAlliance.com, oneWorld.com and SkyTeam.com. all three sites show airlines that partner with others and may have frequent-flier seats available. Miles earned on Continental, for example, may be redeemable on one of the dozen or so StarAlliance members, and vice versa.

Flying high: How to get the most out of your free air miles