(NECN/NBC News: Chris Clackum) - There's something you need to start doing, even by this weekend, that you'll be glad you did when the summer vacation season arrives. And what you need to know is that millions of others have already started.

It's not even mid-January; most of us are far from making vacation plans for this summer, but maybe we should, especially if it involves a vacation rental because bookings have already begun.

"Just in the past week, over 40-percent of properties on FlipKey have received inquiries for June, July and August," says FlipKey.com co-founder Jeremy Gall.

FlipKey.com is an online marketplace for 170,000 vacation rentals at 8,000 destinations around the world.

Renting a vacation home for a week or two, sight unseen, can be risky, though.

So, there are steps beyond making the initial inquiry.

"Do the research," says Angie Hicks, founder of Angie’s List.

She says read reviews of those who've vacationed there before and make a few phone calls.

"Because you want to know that the person you're renting from is reliable and has a good reputation... That they're going to be there in case something goes wrong in the house," she says.

Also, read the contract carefully, which will spell out more than how much you pay.

"The contract will include things like whether or not you need to bring linens or linens are going to be provided at the house," Gall says.

"Are they going to have dishes in the kitchen stock so that you can use their dishes or do you bring your own" asks Hicks.

Both say don't pay in full up front. Make the minimum deposit. Plus...

"And to the best that you can, always pay with a credit card," Gall says.

"By paying with a credit card, you can actually stop payment or dispute the charge if something goes wrong."

Properties in beach cities will likely fill up faster as more and more vacationers choose homes over hotels.