With planting season in full swing across the country now, a simple way to ensure continual bloom all growing season long is to do what I call a "color layout".
By roughly mapping out your garden and then adding trace on top, proceed to color in only what would be blooming during the particular season. Continue adding a piece of trace for each growing period from late spring, to winter. By doing this a pattern will appear and you will be able to see where you would be lacking hue and balance in your garden and where you need to add to ensure continual color through out the seasons. This can be done with not only your perennial borders but with shrubs and trees as well.