When I'm looking for ideas for composing, I often start placing notes in a pleasing order, then work from there and back it up with either counterpoint or harmony. Most often harmony. Usually, I try to get a mental image of what I want the song to represent, its mood, if it's major/minor, etc. then I start. I usually start by making the melody, then I back it up with counterpoint or chords/harmony. But I have made it work before by putting in chord progressions, then builing a melody on top of that. What do you do when you start composing?

Good question! Hmm, I don't really know what I'm thinking of when I start a song . . . I suppose I try to think of a mood or an idea, and then I recreate it on the piano. I usually think up both the melody and the harmony at the same time (makes things easier), and if needed, I'll throw in a little bit of counterpoint. When I'm working with multiple instruments, I consider what parts they play, and how they'll interact.

EDIT: How do I get my ideas? Inspiration!