How could I spend less time on my xbox?

Hey, Im pretty much a 360 addict – play CoD MW2 on weekends and school nights.
Im actually a pretty social guy & spend my weekend afternoons out then spend the night in. But I have important exams coming up in the next two months (GCSE’s) and need to ‘knuckle down’, get off the box and revise – I truly am hooked, and need help/advice to get off it!