You already know that it is advisable to prune any and all dead diseased and damaged limbs, branches, vines - that's a given. Oh, and snip out tree limbs that cross or rub, too.
But flowering shrubs and vines are confusing to keep track of if you have several types. Hydrangeas in particular are challenging because some varieties bloom on old wood and some bloom on new wood.
(The photo is this morning's new growth on a clematis vine that blooms dark purple.)
Here are excerpts from a column on spring pruning by Pat Howell who writes the "Easy Gardener" column for the Tacoma Silver Spring Voice in Maryland. (Click on the link to read in full.)
Some plants like to be pruned BEFORE they bloom because they bloom on new wood - that is, they form their flower buds now.
Some shrubs bloom on old wood - they formed their flower buds last fall.
Right now Azaleas have this year's buds and so you would not prune until AFTER they bloom.
Hard pruning With sharpened hand pruners, or sharp loppers, cut back the following shrubs:
Beautyberry [Callicarpa]—to short stubs
Bluebeard [Caryopteris]—to short stubs
Butterfly bush [Buddleia]—to 10" above ground
Bush clover [Lespedeza]—to 10"
Ninebark [Physocarpus]—to 10"
Smoke bush [Cotinus]—to 10"
St. John's Wort [Hypericum]—to short stubs
Twig dogwood (red or yellow)—leave them until end of winter; then trim back to 12".
Ornamental grasses—to 10"
Winter Jasmine—to 24" after bloom is over.
Clematis vines—Snip away dead stems ABOVE a visible bud. If you do not see any visible buds, wait three weeks, for some more warm weather, to determine if vines have survived. Be careful not to cut through a stem that might be below a bud. If in doubt, wait.
Hydrangea vines—Only prune off branches that are in your way
Crape Myrtle - After you see leaves, it is safe to do some shaping by cutting out stems simplifying the trunks into groups of three, or five at the most. Be sure all leaves and twigs are removed way up (usually above your eye level) to enable the spectacular bark to show. This pruning will promote much more of a flower display.
Nandina—Snip off dead leaves and twigs.
Prune after bloom
It is best to prune some shrubs in the two months immediately following their bloom. By mid-to-late June, new buds are forming, even if invisible to us. Don't plan to prune after June 15.
Including: Azaleas, Deutzia, Forsythia (cut them to 12" high and wide right after flowering), Flowering Quince, Lilacs - cut off blooms as soon as they fade, Hydrangeas (most, though not all, bloom on old wood). It is hard sometimes to keep track of which blooms on old vs. new. If you are not sure and your plants look ratty, cut off the ratty/dead tips, and wait to cut shrub way back until after bloom.
Overgrown shrubs may require hard, selective pruning after flowering. You may want to restore plants that have grown too large but wait before seriously attacking old shrubs, until they have had a chance to recover from February's weather.