Dig a square hole instead of round if your soil is clay. 
Water well with a hose the day you plant and for several days water every day. Then water every other day for a week or more and then every 2 days for a while. All along this hose watering install the drip system focusing on the edge of the outside of the original rootball. Use a 24" probe moisture meter to learn what the soil moisture is doing down lower than your finger can test. We like the one sold by Lincoln Irrigation.
https://lincolnirrigation.com
Water where the roots are today.... near the outside of the root ball and also one foot outside that for where you want the roots to grow - outward. Roots will also grow down. Amend the soil outward from the trunk and add compost and mulch on the top to feed the tree in the future.