Creativity happens through weird restrictions.

Tell students to "write a story".  They won't have many ideas.

Give students structural restrictions such as a minimum senetnce length or requirements to use specific vocabulary or grammatical structures and they will come up with something, but it won't be very creative.

Give students a creative restriction such as "your story must have a pair of gloves in it which one of the characters must use, but not to put on his/her hands"  and suddenly the creative possibilities are endless.

This works with art too.

Tell your students to "build a machine".  They won't have many ideas.

Give students structural restrictions such as the requirement to use exactly 10 legos, 4 of which must be blue and they will come up with something, but it won't be very creative.

Give students a creative restriction such as "you only have one lego piece with wheels, but there are only 2 wheels and the piece won't balance by itself" and suddenly the creative possibilities are endless.