Like I said in the other thread, once you pick a key (based on what your goal is for the track) you can just write out your scale, write a few chord progressions based on your key, write some arpeggios... once you do that just pick out root notes and of chord progressions and the arpeggios and do a rhythm based on your drum track and the song arrangmement, you know like is it a build, or a drop, or a breakdown... let that dictate the cadence