For plants that flower in spring or early summer AND lose their leaves in winter (deciduous plants), now is the time to prune unless you only planted them this year.
Pruning immediately after flowering allows the maximum time for development of young growth to provide next year’s flowers before the end of this summer.
Pruning requirements depend on the type of shrub, but all early-flowering shrubs need routine removal of damaged, diseased or dead wood. To do this you simply…
Cut out any damaged or dead branches back to their point of origin or to ground level.
Where the plant is really bushy and has many stems, remove a few to ground level anyway to open it up and avoid congestion.
Remove any weak, spindly or twiggy shoots right to the point of origin or to ground level so the plant focuses its energy on strong new shoots.
You should then follow the general guidelines for your specific plant.
Deciduous shrubs with flowers on strong young growth such as Forsythia or Weigela Cut back flowered growth to strong young shoots lower down. Each year cut out up to 20 percent of older stems near the base.
Deciduous shrubs producing new flowering growth from or near ground level like Kerria Remove flowered shoots back to a vigorous sideshoot. Cut back one in three stems to ground level each year.
Deciduous shrubs that respond to hard pruning after flowering like Prunis triloba Cut back all the stems to near the base.