Read the book called
How to Become A Straight-A Student... Make lists, use a calendar religiously and profit.
Study: 15 hours/week (20 max)- As you will learn in the book, efficiency is key. I used to sit around and "study" for hours on end (sometimes up to 8 hours a day...), when really I was on Facebook, texting or trying to "multi-task." Just sit down, focus intently on a single task and knock it out so you don't have to worry about it anymore! That book changed my life.
Class time: 12 hours/week
Work: 50-60 hours/week (definitely not by choice)
ECs (shadowing, volunteering, etc.): 7 hours/week
Hobbies: 10 hours/week
Commuting (sucks): 8 hours/week
Being an adult (cleaning, running errands, eating, etc.): 15 hours/week
Sleep: 6-7 hours night