Key is to regularly water newly-planted trees, at least bimonthly for two months. It is also important to ensure you choose a location where your tree has enough space, which you can calculate from a variety's eventual height and spread.
Bare root & containerised trees have different planting requirements. With bare root, it is important to soak your tree's roots in water for up to 2 hours before planting, while with containerised trees it is important to drench your tree's rootball. With bare root it can be useful to prune woody roots back a few inches, while with containerised trees, it is important to free any spiralized roots growing around the rootball's circumference. With bare root trees, dig a hole so as to ensure the graft point is above the soil, while with containerised trees, ensure the pot sits no lower than an inch below ground.
Bare root & containerised trees also share planting requirements. Dig a hole twice the radius of the rootball. Stake your tree no more than 2-3 inches from the stem, pointing away from the prevailing wind. Fill the hole with a mix of compost and garden soil, and add fertiliser and mycorrhizal fungi. Do not compress the soil. Give your tree a good watering. Add mulch on top whether bark and wood chippings, compost, manure, leaf-mould and stones. Make sure mulch doesn't touch the stem. Tie the stake to your tree, leaving space for growth. Place a rabbit guard around your tree.
Apply fertiliser and replace decomposed mulch come spring. Check ties to ensure there is no rubbing. Collect fallen leaves in autumn.