My motivation tip for losing/maintaining weight: Set a certain daily average you want for an amount of exercise (i.e, 10km of running or 15km of cycling etc), and then keep a log on your computer or a piece of paper and write down how much you do each day. If you miss one day, then you have to do more in the next couple of days to get the average back up! The motivation through the day is to do your exercise, that way you won't have to do HEAPS of exercise the next day.
And also, if you set up your log in a table kind of style and set an amount of days (i set 30 days up), once you've finished the log and its time to write up a new one, you can set yourself new goals. That's important because, unless you've been doing the same or more exercise for a long time before, you're going to get more fit and be able to handle much more exericse.
I started on 7 - 8 km of cycling 3 - 5 days a week on this log thing and now i average 15km EVERY day, and am in better shape than i've ever been.
As for study, i have nothing
I've been terrible since year 12 started.. need some motivation to