I have several different composing modes:
I - I sit at my piano and just put my hands down and play something. If I like what I hear I write it down in my musical journal under the correct catagory (I usually catagorize by emotions suck as happy, sad, joyful, ect.
II - I sit at my piano and play chord after chord till I find a progression I like. Then I play around with different inversions until I think its perfect. I then record it in my little notebook, so later I can...
III - pound on my snare drum until I find a rythm I like. then add simple chord tones as the melody
I rarely work with scores... and when I do that I'm just arranging/orchestrating what's already in my notebook.