Best advice I got on composing:

Treat each voice as its own personality.

I'd call that advice on "harmony", or "arranging", not on "composition". As far as composition goes, harmony is not the most important factor.

Personally, I've never had any advice on composition. I just composed, right from the start - learning as I went along by learning play lots of other music.

I guess if I was to give any advice now, based on my experience, it would be:

Keep it simple. Focus on melody (and lyric if writing lyrics). Make the melody singable and strong (even if instrumental). Keep the harmony straightforward; add complexity here and there if you want, but never let it distract from the melody.

/r/musictheory Thread