Before you attempt to prune your climbing rose, you have to be certain that it is a climbing and not a rambling rose type! A quick, more or less fail-proof test, is to ensure that your climbing rose has its leaves in groups of five leaflets.
Once you establish that you have Climbing Rose and not a Rambler, then follow the pruning advice below.
For the first two or three years after planting, your new climbing rose will not require any pruning. During this initial period, your climbing roses should send up a few long stems, which can be trained into a basic framework for your future climbing rose's shape.
The annual pruning of your climbing rose takes place once you have the basic framework.
Try to get a framework of stems trained horizontally along wires or trellis framework. There will be more rose flowers from horizontal stems than vertical upright stems.
Once you have a framework of horizontal stems - after two to three years - then you are into the regime of pruning your climbing rose each year.
From the horizontal older framework of branches on your climbing roses, you will find new shoots will sprout along the main branches from early spring. In early summer - or right after flowering, if they flower - cut back these shoots to within 4-6in of the main lateral stems. The new shoots that then grow from these pruning cuts, will be your flowering shoots for next year. Depending upon variety, these new shoots will grow to around 10-12in and produce flowers early summer the following year.
Climbing roses flower best on stems that were produced the previous year, so pruning of your climbing rose each summer is important if you are to obtain the best results for the following year.
The images below can be enlarged by clicking. Left image shows climbing rose immediately after flowering - note the recently flowered growths. Right image, shows how the rose will be pruned in order to get more new shoots for flowering next year.