Check Your Soil Before Watering and Water Carefully
There's no magic formula for how much water to give your tree in its first year, so don't rely on a “rule of thumb” for watering. Too little water can kill a tree. But overwatering in clay soil can cause root rot, which can also kill a tree. You'll need to water your new tree until the root system is well established. The right amount of water depends on the weather conditions, your soil and the planting site. The most reliable method for knowing when to water is to stick a popsicle stick (or your finger) 2 to 3 in. into the ground. If the soil is damp down 3 in., you're giving it enough water. If not, water once or twice a day—whatever's needed to keep the soil damp but not saturated around the root-ball. Allow the soil's surface to begin to dry out between waterings.
For the first few weeks, you may have to water every few days depending on the weather. After that, longer (deeper), less frequent watering is much better than shorter (quicker), frequent watering. To help the tree create deep roots to resist drought and wind, encircle it with a soaker hose a few feet out from the trunk and run it on a trickle for an hour.
Match the Tree to the Planting Site
Plant a tree that will grow well given your hardiness zone, existing soil conditions (test if you're not sure), sun exposure and available moisture. Tree species that are native to the place where you live are probably well adapted to the climate in your part of the country. If you're planting a nonnative species, research its site requirements carefully.