If your tree has been cut 8 hours or more before being given water, make a fresh cut about 1/2 inche off the bottom. This will remove the dried sap that has sealed the pores and allow your tree to drink.
Avoid using a stand that is to small and requires whittling the tree down. The outer layers are most efficient at absorbing water.
Place the tree in water as soon as possible. Most trees can go 6-8 hours after cutting and still take up water. Check the water daily.
Use lights that emit a low amount of heat, such as LED or miniature lights. This will reduce drying the tree. Additionally, don't overload your tree with lights and turn them off when you're not at home or at bedtime.
Fireplaces, vents, direct sunlight, heaters and such can be a fire hazard as well as drying out your tree more quickly.
All of the above tips will help keep your tree fresher longer. However, it will eventually dry out. Once the tree is very dry, it's time to remove it from your house. Never burn your tree in wood stoves.