well that depends on the period-style of your current composition. are u doing a 20th century or a baroque composition?
Try to go for contrast between the pieces. Sometimes I like to think of characters, scenarios, images, etc. when I play miniature improv sets. Do you feel a link between key and colour? You may wish to use that as well. Try improvising in a certain key if you are at a loss of ideas. Certain things may poke out as being unique or easier to play. Use the keyboard topography, as inspiration.