As you drive around the Athens GA area, you will notice many homes that have had their Crepe Myrtle trees severely cut back. There's a lot of misconception among home owners with regards to Crepe Myrtle pruning. Some people will tell you they have to be pruned in order to flower. Some will tell you hard pruning will increase the number of flowers, and then some just want them pruned because they see everyone else doing so.
The truth is very little pruning is needed and hard pruning year after year can lead to early decline of the plant. The larger the cut, the greater the chances of decay entering. They will flower regardless of pruning or not.
What I recommend is to snap of any tiny twigs, remove suckers, and try to not prune anything much larger than about .5 - 1 inch.
And lastly, when thinking about planting a Crepe Myrtle, choose a cultivar that is best suited to the planting space. This day in age, Crepes come in all sizes. If you have a spot for a small to medium size tree, don't plant a variety that want to grow to a massive 25-30 feet.
Crepe Myrtles are very forgiving and beautiful trees. With proper care techniques they will be a long lived and enjoyable part of the landscape.