How to increase the quality of my sleep?

I just turned 16 and got more hours at my work as a cashier at the grocery store, and if I thought it was hard to cram in 1 hour of guitar, an hour or 2 of COD, a couple hours for studying my AP US History book and all the time in between that I have to watch the puppy so she doesn't pee on the floor and still get enough sleep so I can be awake enough to not fail my tests the next day, it's impossible now. I realize getting more hours of sleep isn't going to happen (and even when I do, like on weekends, I still feel dead the next day), so I thought maybe I could increase the quality of my sleep instead, like getting more REM sleep or whatever. How can I do that?