Metaphors in art can be obvious, I think of the target pieces that both Beans Gildorf or Mary Ann Jordan have made, or much more subtle and personal - I'm reminded of the broken circle quilt in an early Quilt National made by the lady (so sorry I forget her name, please comment if you know it) who was dying of breast cancer.
An interesting design exercise would be to sit down with an issue - personal or general - and think how many ways could I depict this delight, this joy, this sorrow, this concern, this issue etc.
A new grandma could make a wonderful piece based on drawings of tree buds - full of swelling promise. Both more subtle and more universal in meaning than a flat Bubble Jet set print of the new babe.
Having got the urge to make a piece about X or Y (and you know how fascinating X and Y can be!) - don't be too literal - think how many ways could I depict the idea, thought or feeling? Stand back and sort through them and don't be afraid of Metaphor!
here are some examples from my work: