muahha. i always left my compositions to the last minute. as in, the day before it was due o__O;; i mean, i'd already had ideas and stuff that i'd written down, like an alberti bass or whatever, but ahah i never learn
so i highly recommend you get started on the ASAP. your teacher should be willing to help you as much as s/he can. my music teacher, bless her, actually came over to our houses a few days before we had to submit our compositions to the Big Wigs, on a saturday, and helped us. gotta love her.
problem with my compositions was that they all sounded kinda similar
not that my teacher really cared. the way i composed - sat down at piano. play a broken chord in left hand. played a melody in right hand. voila! i came up with some really good melodies sometimes but as soon as i got up to get a pen and paper, i'd forget it -___-;;;