What is a Motif?
An idea or object that repeats throughout a story to support a theme.
For example, if death was your motif, you could repeat the word or use related words like funeral, or grave, burial.
Motif vs. Symbol
A symbol represents something else and can become part of the motif. In the movie The Sixth Sense, director M. Night Shyamalan uses the color read to represent death (a door knob, a flower, clothing, etc.).
Motif vs. Theme
Theme is the underlying message of your novel. Use motifs as breadcrumbs to help lead the reader to it.
Examples
In A Tale of Two Cities by Charles Dickens, imprisonment serves as one of the motifs.. Every character faces it in some way.
In To Kill a Mockingbird by Harper Lee, of old-fashioned small-town values serve as a motif.