Organization.

Two AP classes, three varsity sports, speech, drama, and a job. At the beginning of the year, I also had another job on top of all that, so one could say I have some experience scheduling. During the summer, with two jobs that always conflicted, stressful did not even begin to describe the situations it had put me under. Even with a detailed planner and a color coordinated calendar, stressed-induced stomach pains filled a couple of weeks of my summer. Now know that this is not an argument against being involved, that is the complete opposite of what I would advise. The two jobs is the one thing that got me into trouble, so if you gain any knowledge from this post, do not get two jobs in high school, it is not worth it. And back to being involved, get into as many things you can without overwhelming yourself. There are so many opportunities in high school, search for every one that interests you. The busier you are, the more organized and focused you have to be. The more free time you have, the more time you have to slack off. Being in so many activities, the responsibilities that I have placed upon myself, in my opinion, has better prepared me to face what ever obstacles life has to throw at me.
On to how I possibly fit everything into a 24-hour period. First, prioritizing is key. School should obviously come first, so make sure to plan times to get homework and studying in, because with as busy of a schedule as mine, the snowball effect becomes twice the size of the avalanche. Having a color coordinated calendar and a planner is also a necessity. If I was not able to write everything down, my days would spiral out of control. Here is a tip, every time you tell yourself, "Oh, I will just remember it." JUST START LAUGHING and pick up a pen. Even if you do remember everything, it always helps me get through the day when I can cross things off my list because I know when I am done I can get to what is the most important part of my day, sleeping. Make sure you schedule that in with all the other things, some of the best days I have are the ones that I know that I am getting more sleep than usual. Now, I have mentioned my color coordinated calendar multiple times, and I hope you have realized its importance to me. Now color coordinating works very will for me, the bright colors makes the long days a little brighter, but if it does not work for you, I will not be offended.
From one busy bee to the next, good luck with your future endeavors, make time for yourself, and know that it is possible to be extraordinarily busy and still enjoy ever moment of your high school career.
JSL