Autumn is an ideal time to rejuvenate a deciduous hedge, stimulate root growth and keep it looking good through the following spring and summer.
For evergreen hedges, it is best to leave them until spring, especially conifer hedges or you risk getting bald patches!
When you are cutting your hedge, keep the base wider than the top, this prevents the top shading out the branches at the bottom. Ideally you should leave at least 30 - 40 cm gap between a hedge and other planting, this reduces the competition for root growth and provides a handy access path.
It is also a good idea to prune the top of the hedge one year and then the sides another year, this ensures you get some flowers and berries each year which grows on the old wood.
Hedge cutting is best avoided during the bird nesting season (1st March - 31st July).