This is good for middle schoolers, high schoolers, and even college students. It offers valuable information as well as strategies like a place to fill in your schedule to see where your time goes.
Another site about using your time wisely, this time mostly for adults.
Remember the Milk is a site for easily managing your to-do's. They are still working on it so it may take a little bit of time to learn, but it is all worthwhile. The goal is to write everything you can think of down so that your mind is free to pick which things are most important.
Well that's all for now. I hope you found these links helpful!