When the weather gets colder, the leaves start falling. When the leaves are gone, people really start to notice the limbs on their trees. That's why a lot of people decide to prune their trees around this time of year. Crape Myrtles are a often targeted. They are relatively short compared to large trees, such as oaks, and their limbs tend to look a little messy. Unfortunately, crape myrtles are often pruned incorrectly.
Let's get this out of the way first. Do not "top off" your crape myrtles. It shortens their life, leads to disease, and distorts the way they will grow in the future. To be honest, an assortment of crape myrtle trunks sticking out of the ground in the winter looks pretty awful. The practice is called pollarding and is only appropriate for a select few varieties of trees that are grown further north.
Only prune crape myrtles to enhance their natural shape. More often than not, your crape myrtle does not need to be pruned. If you have crossing branched, one of the two has to go. Prune away weak or diseased branches. Low hanging branches should also be trimmed. Remove any lingering seed pods from the warm season. Also remove any sucker growth whenever it occurs. An exception is when a tall variety of crape myrtle is planted to close to an over hanging roof. You will need to cut this back every year so it doesn't damage your property. It will look worse each year. To avoid this, replant with the correct sized crape myrtle species.