Music Composers Unite!
For what it's worth I do the following:
1. Decide what I'm going to compose (e.g. Military Quick March, waltz, choral piece, concerto)
2. Decide for what instruments I'm writing (a Military Quick March answers its own question about orchestration whereas a waltz could be for any combination, or even a solo instrument like piano)
3. Decide what key to write in (different key signatures suggest different moods to me)
4. Compose a strong, memorable and attention grabbing opening (I often listen to new music but switch off if the opening doesn't grab me)
5. Utilising the thematic motif(s) from the opening, develop them logically through expansion, diminution, augmentation, transposition and any or all of the musical developmental techniques available - basically aiming for coherence but also with just the right amount of development to hold the interest of the listener (i.e. don't be boring)
6. Aim for a musically excellent ending that brings the music to an emotionally satisfying and logical conclusion.
7. Consider throughout the compositional process the effect that what I'm writing will have on the ears of listeners (I generally have an idea of the type of audience I'm writing for)
8. Play what you've composed many times and don't be afraid to make adjustments no matter how major and time consuming they might be.
9. If I am not completely satisfied with what I've done I will shelve it for anything from 24 hours to 5 years and then make further adjustments.
10. Publish it.
10. Don't expect everyone to like what you've written - you can't please all the people all the time.