Writing a theme or a melody for a piece for me is an intellectual work, a lot of analysis.

I think of a theme as of a person and search for a better way to describe its character. In music for that we have three basic tools: Melody. Harmony. Rhythm.

Where the second one can be seen as a melody: harmony notes played separately become a melody.

Let’s say we need to describe a character who is: powerful, dangerous and unpredictable.

We translate those qualities into Pitches (Harmony and Melody) :

– Powerful: strong and large intervals like fourths, fifths and octaves

– Dangerous: minor second, augmented fourth and major seventh

– Unpredictable: irregular use of those intervals will give uncertainty to the music

and Rhythms :

– Powerful: steady, accented and not too fast note duration.

– Dangerous: some sharp and sudden accents and rhythms.

– Unpredictable: irregular use of those tricks will give uncertainty to the music.

This is a pretty straightforward and easy way to create characters. But it works well and listeners will get your point.