Within the inventory of the perennials that will grow in a specific part of the garden... I first want to find a plant whose foliage will contribute color, form, and texture... and work well with already installed plants. The blooms are great... flowers are always great... but flowers are fleeting on most perennials and foliage lasts the season.
Keeping to that approach has helped create at least what I think of as a good combination.
But that isn't stopping me from aiming toward more blooms this year.