What is the right way and appropriate time to prune a potted rose plant?

PRUNING: Hybrid Tea roses and Floribundas should be pruned down hard in January. These roses bloom on new wood, so proper pruning encourages more flowers and also helps prevent diseases from wintering over. Climbers and arching shrub roses should not be pruned so severely, since it would destroy their naturally elegant shape. Remove any dead or weak wood, and thin the plant to maximize air circulation and sunlight. Once-blooming roses should be pruned in summer, right after they have flowered. Most roses benefit from being completely defoliated in winter, to encourage a deeper dormancy and to remove diseased tissue. Climbers and arching shrubs should be trained to grow horizontally or diagonally, since vertical canes will only bloom on the tips. Training encourages flowering lateral shoots to develop all along the canes.

Roses can be pruned anytime. although if it looks like its going to flower I would wait until it has bloomed. Then depending on the time of year cut back to the next set of lateral leaves/ branches and it may bloom 2 x's. At the end of the blooming season you can do a heavy pruning just don't go to low because all roses are grafted and if you cut below the graft your rose may not bloom again at least with the flowers you were hoping for.Have fun