Cut them back half way and this will spur new growth, which keeps them bushy and productive. If you didn't pinch the flowers while they were in bloom, then cut them back by one third. It's best not to prune them late in the season.
They hold up very well in a vase. For best results, strip the leaves that will fall below the water line and don't wash the herbs until you are ready to use them.
My bouquet contains rosemary, pineapple sage, ciliantro, chocolate mint, sweet, purple, and variegated basil, chive blooms, and hibiscus.