as the other said, gently break apart the root ball and make sure you've got a hole large enough and that the soil is loose enough so that the roots can grow through it (amend if necessary).
when watering a newly transplanted
plant, make sure to water not just right at the root area right below the
plant, also water at the 'drip-line'.
this is the circular area that lies below the out edge of the leaves on the
plant. do good deep waterings of the drip line and the roots will reach out to get the water...helps the
plant form a sturdy root system.