The should be pruned just after the harvest period.  Pruning too late in the season may remove the latent buds that would become the next round of flowers and berries.  Feeding helps too although not in the heat of summer.  Holly-tone in very early spring.  Keep them watered too, they like cool soil and have a shallow root system.  Mulching helps to just keep the mulch a few inches away forn the stem where it enters the soil.