Late autumn or early spring is the best time to transplant most dormant plants. Plants, with the exception of bare-root, can be transplanted at anytime between when the ground thaws and when it freezes (so anytime if you are in a frost free climate). However, if transplanting in the heat of summer, you'll need to be diligent in watering and provide extra shade for your plant in the first few weeks after transplanting.
Dig a hole 2-3 times the width of the root ball. The hole should allow the plant to sit at the same level in the soil as it was previously. Fill the hole with soil ensuring that the crown of the plant, where the roots and stem meet, is level with the soil surface.
Plant out in the early morning or evening and/or on an overcast day. Avoid planting at peak sun times or on windy days, this will allow your plants to settle in comfortably and protect them from windburn and sunburn.