The Crape Myrtle is a Sun worshipper. It performs like a pro in sunny, hot areas. When planting, be sure to give them a large area to spread. When given an ideal location, they will put on a spectacular show of color, an plumage, almost year round.
To help your Crape Myrtle gain a particular shape, start at the base. Remove all but three to five shoots. As the tree matures, remove lower, lateral branches one-third to halfway up the height of the tree. Remove branches that are crossing or rubbing against each other and shoots growing into the center of the canopy. Make your cuts to a side branch or close to the trunk. Head back wayward and unbranched limbs. As it grows taller, remove lower branches as needed. Remove any future growth from the ground to retain the desired tree shape. This basal sprouting may occur whether the tree is being pruned or not. Pull these out when succulent instead of pruning them.
You will notice some seed heads forming, in late Winter, or early Spring, and may have the urge to pluck them. This is not necessary. It will benefit, nor harm the tree to do so.
When you are faced with a much older tree that is in need of maintenance, you will basically do the same thing. Limb up, to remove obstruction of doors, or windows. If the Crape Myrtle is too close to a structure, consider removing one of the major trunks. Avoid cutting the top out, or 'topping', an aging tree.
To maintain the height of a Crape Myrtle, prune it moderately, by moving all twiggy growth back to lower growing side branches. This will unify the tree.
Corrective pruning is useful to promote a healthy tree. If you see a problem area, or dead branch, remove it immediately. All other times, simply prune by removing lateral branches, small twigs, or obstructing branches.