carefully if it's thorny. I prune my Flori or HT climbers in early March. then during the summer months, I bring the new growth down to a vertical line. I dead head regularly. With all my, shall I say rampant, ramblers I cut them down to 4' in the late winter. And then try, and I do mean try, to tame and control them during the summer.

With modern everblooming climbers, chose 4-8 of the youngest major canes as the main structure of the plant, and cut out all the rest, including those older than 4 years. Cut the side branches of those you save back to 3-4 buds, and train the canes out in a fan pattern, making them as spreading as possible, or even arching them--they bloom better on the horizontal parts. The best time to prune is in early spring, just before the buds would sprout.
With spring blooming ramblers, prune them severely right after they bloom, since they bloom on growth produced the previous year.