NEW YORK — To snag the best airfares, travelers need to be adventurous and willing to pick up at a moment’s notice.

OK, now let’s be realistic. Most people making summer travel plans need just that: plans. They get a week off, maybe two, and aren’t going to spend hard-earned cash on a last-second whim.

But great deals are still within reach for those who have even a little flexibility in choosing where and when to travel.

The average roundtrip domestic ticket will cost $431 this summer, an increase of 2.6 percent from last year, according to Kayak.com. But remember: that’s an average. One trip might cost $800 while another can be found for $200.

“Airfares are high but there are pockets of cheap out there,” says Seth Miller, an information technology consultant who writes a blog under the name The Wandering Aramean. Miller does his best to beat the system by connecting in strange cities, flying at off hours and taking advantage of sales often offered when an airline adds a new destination.

Here are some tips from Miller and other expert travelers on how to combat rising airfares.

— LAST-MINUTE WEEKEND FARES

When airlines don’t fill planes for an upcoming weekend, they slash prices.

Each Tuesday, they email offers for that coming weekend or the following one to fliers who have signed up online for the deal alerts. Travelers have to depart late Friday night or anytime Saturday and come back Monday or Tuesday. An added plus: weekend getaways save precious vacation days.

Recent offers include: Houston to Memphis for $180, Huntsville, Ala. to Chicago for $174, Washington D.C. to Greenville, S.C. for $157 and Charlotte, N.C. to West Palm Beach, Fla. for $240.

— TWITTER AND FACEBOOK

Airlines are experimenting with sales on Twitter. At the forefront is JetBlue, which tweets last-second fare sales and vacation package discounts from (at)JetBlueCheeps. Some deals apply to just a few seats and are gone within hours.

“If you find something, jump on it,” says John DiScala, who each year flies around 150,000 miles, visits 20 countries and writes about it at JohnnyJet.com.

JetBlue recently tweeted a sale at 3:16 p.m.; it ended at 6 p.m.

Airlines announce special sales to those who “like” their Facebook pages and sites like AirfareWatchdog offer fare alert emails (airfarewatchdog.com/fare-alerts/).

There are also frequent fliers who search for and post cheap flights in online discussion boards. Two of the better discussion boards are: http://www.flyertalk.com/forum/mileage-run-deals-372/ and http://milepoint.com/forums/forums/mileage-runs-mattress-runs-travel-hacking.6/

— FLEXIBLE DATES

Looking to go to Paris for a week but don’t care when in the next few months? ITA Software’s airfare search (matrix.itasoftware.com) provides a calendar of the lowest fares.

Just enter the departure and destination city — nearby airports can even be added — and then how many nights to spend there. It will find the cheapest prices for a month out from a given date. The length of the trip can even be a range, say five to seven days.

— CHASE THE FARE, NOT THE DESTINATION

Want to know the cheapest fares from a departure city to anywhere? Check out Kayak’s explore tool (kayak.com/explore). It allows travelers to search multiple airlines at once this way. A map pops up with all the destinations under a set budget point.

Searches can be done for a particular month or for all of summer. The query can be narrowed by activity — beach, golf, gambling, skiing — or by continent.

— ODD CONNECTIONS

Fares to Hawaii might be steep. But connecting though another city with a sale to Hawaii, could save a lot of money. Use AirfareWatchdog’s “fares to a city search” (airfarewatchdog.com/cheap-flights/to-a-city) to see if there are any less expensive indirect routes to your destination. Instead of flying from, say, Boston to Honolulu, it could be a lot cheaper to book two separate tickets — the first between Boston and Houston and the second from there to Hawaii.

“If you can save $1,000 per couple and get two cities for less than the price of one, it’s a no brainer,” says Georgia Hobica, founder of AirfareWatchdog.