#1 - Make a Game Plan
It can be easy at the store to forget that your kid has a surplus of jeans and what their wardrobe really needs are a couple of pairs of nice-looking khakis, so it's a good idea to plan out a few priorities beforehand. That way you'll know where to steer them as you're sailing through a sea of clothing racks.
So open the closet doors and dresser drawers wide and start sorting items and evaluating what kind of shape they're in. Then count what's left and decide where you need to focus your shopping dollars.