Proper Crepe Myrtle Pruning
Below are two links that provide valuable information about proper crepe myrtle pruning. Too much pruning will negatively affect the growth and appearance of crepe myrtles and they will not produce as many beautiful blooms.
So before you pull out the garden tools please check them out.
http://www.wilsonbrosonline.com/How-To/Pruning-Instructions/How-To-Prune-A-Crape-Myrtle.aspx
http://www.walterreeves.com/landscaping/crapemyrtle-pruning/