Book your rental early!
You don't want to miss out on the available week at your dream rental.
Know about the rental as much as possible.
Almost all rentals come with kitchenware but not all with internet access. Make sure that the rental you're interested in will accommodate the needs of everyone in your party.
Find out about the local area and things to around town for possible rainy days. Or if the listing says "hideaway" or "quiet" then see if the distance to places like the grocery store is to far. If the opposite is mentioned then be aware of the pros and cons.
Contact the owner.
If you have any specific questions, contact the owner directly. Rental agencies just use selling points so they can take your money in commissions.
Time is money
Renting early, late, or offseason will get you the best rates possible.
Examine the pictures.
Look for things that might spark your vacation experience. When you look at properties pictures, can you picture yourself having a wonderful time?
Read the listing carefully.
Some owners have potential to be salesmen, but is their rental all that it says it is? Watch out for words like "Luxury" (what amenities actually make it so), "Cozy" (usually smaller than advertised), and "Perfect" (we all know nothing is perfect).
Research the weather.
Most popular vacation spots have drastic changes in climate throughout the year.
Be sure that there will be enough to do during your stay. Nothing is worse than paying to be bored.
Be patient in your search.
Don't always go for the first rental you see. Sites like vacationcentric.com allow you to view many rentals with the click of a mouse. There're many rentals available online so know your options and choose wisely.