Plz help, how to control oneself?

iam studing now in tenth standard. i ranked frist in my cl last year. i always study a week or two before exams and i score really well. but this time in tenth everyone studys dialy and i have fear in myself whether i will do well in exams. and i also get diverted by t.v and computer games. when i was in ninth i come home from school do my home work just p time watching t.v. but this time doing the same thing pricks me and i feel wastage of time. even though i know it i can't help it out. what should i do ????