Most plants benefit from regular feedings during the growing season. Use a good balanced fertilizer in one of several forms. A good balanced fertilizer often does wonders to increase growth and enhance flowering. Remember compost is also a source of nutrients. Using a fertilizer high in phosphorous but lower in nitrogen will help flowering species reach their full potential without focusing too much on leaf growth.
Most perennials end up spindly and unattractive when high-nitrogen fertilizers are applied.
Assess which plants need to be pruned. Some plants need pruning to control spreading and guide new shoot growth. Some plants need pruning to refresh and increase new growth or to remove old or damaged parts. Either way, the process is the same. Decide which shoots need to be cut, and figure out how far back the plant should be pruned.