Someone talk me through pruning rose bushes properly?

Late winter or very early spring, just as the buds start to swell - that's the window for most bush roses. Start with the three Ds: anything dead, damaged or diseased comes out first, back to healthy wood. Then take out stems crossing through the middle so air can get in. After that cut the remaining main stems back by about a third to a half, each cut just above an outward-facing bud and sloping away from it so rain runs off. Sharp bypass secateurs, not anvil ones, or you crush the stems. Climbers and ramblers are a different job, don't treat them like a bush.