When you bring your tree home, saw a couple inches off the bottom of the trunk before setting in water. When trees are cut, pitch oozes out and seals the pores. By sawing off the base, you will open up the pores, and the tree will be able to absorb water.
Watering is critical. A freshly-cut tree can consume a gallon of water in 24 hours!
Fill the tree stand with water and keep it filled.
Never let the water level go below the tree’s base.
Indoors, keep the tree away from heating ducts or other heat sources. In fact, the lower the temperature, the better the tree will do.
One old Vermonter we knew always packed his tree stand with well-watered soil and planted the tree in the mixture. The soil should be kept wet.
Some people add aspirin or sugar to the water; we can’t say whether either helps. Again, water is the vital element.
For full article, go to the Farmer's Almanac.