Everyone wants to know how to plant a fruit tree. It's not hard, all you have to do is watch somebody do it.
Start by digging a hole twice the diameter of the root ball, and slightly deeper. Like any plant out, water is critical. Water the tree before planting, water the ground, and water again once finished planting.
Before planting add some organic palletised fertiliser to the hole. As the tree is likely to have been grown in a pot, make sure to loosen up the tree roots using strong fingers or a knife, this will allow roots to sprawl outwards rather than bind and constrict on themselves.
Once the tree is in ground, add some fresh compost and top it off with whatever soil is remaining. Be sure to clear away soil from the base of the tree, which can cause the trunk to rot.