Pruning roses is generally done around Valentine's Day. In Tyler, where they have the beautiful famous rose gardens, they prune them back in July (I believe) so they get a bunch of blooms by the time the rose festival rolls around in October.
As for the best method, get yourself some thick gloves and some sharp bypass pruners. It is best to cut the roses off just above where there are 5 leaves on the stem. Make the cut at an angle. If they are antique roses, you may want to leave the spent roses on the bush so you can get some great vitamin C from the hips. That is, of course, if you garden organically.
When doing the trimming, I do not think they should be cut back more than 2/3.