With the normal bush roses - the Hybrid Teas and Floribunda types, there are two times for pruning depending upon your garden situation. The real pruning should be carried out early spring - end of March. In addition to this, there is a form of autumn pruning that is normally desirable.
The autumn pruning of roses simply entails cutting back the individual stems by up to halfway. This is particularly the case if your roses are growing in a spot where they are likely to suffer from autumn and winter winds.
If the roses are left un-pruned, there is a real possibility of the rosebush suffering root damage as a result of being rocked back and forth. There is also a chance of damage to the bottoms of the stem where they join up with the root stock. Slight damage to the roots can cause the rose bush to grow suckers the following year.
Damage to the lower stems can cause disease to enter, and generally weaken the bush. It does not matter how where the cut is made. The real purpose is to prevent wind rock damage. A clean cut with sharp secateurs or loppers is the aim. Wear gloves. The thorns are spiteful!
Pruning proper, is carried out in the spring, and generally means cutting back to within 15cm of the rootstock join. Weak looking stems can be cut back a little further.
The pruning cut should be made cleanly and just above a dormant bud. It does not have to be an outward facing bud as is so often written. That idea was put to rest long ago. In the event, buds will sprout from several places around the pruned stems which then normally allows for a good shape. Any subsequent new shoots that grow inwardly with a chance of rubbing against other growths should be removed as the season progresses
Cut back to within 15cms of the rootstock, and you will have a shape akin to an upturned hand. This will be the basic framework for your rose to grow in the classical ‘bowl’ shape which is desirable to increase air circulation, and in any event makes for a good healthy looking rosebush.
With the larger growing Floribunda types - Queen Elizabeth etc, it is better to make the spring pruning a few cms higher - leaving a stump around 20cm from the ground.
If the spring started before you prune, there will probably be a few new shoots further up the stems. Do not be tempted to make the pruning cut above those. They will probably succumb to a late frost anyway!