[header] How to fit all of your stuff in your tiny locker [title] Figure out a time you can spend on your locker. [substeps] This isn't just something you can do between classes. Try asking your parents to drop you off at school early, or see if you can stay at school late one day to focus on getting your locker in shape. 
You may need as little as 5 minutes to clean and organize your locker, but depending on how bad it is you may want to plan for as much as 20 minutes. Be honest with yourself; overestimating is better than underestimating when it comes to time.