Ensure plants are moist
Dig hole to take container size,
Mix in moist peat & a handful of bonemeal into the bottom of hole.
Plant the rootball level or slightly higher than natural ground level,
Back fill soil around plant.
If planting a tree, make sure that it is well staked & securely tied, this will protect it from the wind until it has established.
Water regularly throughout the season if required as plants need consistently moist soil.