Last year I was horrified at the amount of paper we wasted on "free draw", which is what the kids do when they are done with projects. This year, I set a goal to prevent this from happening. The first thing I did is I stopped letting the kids use blank paper. We started using Doodle Books.
This is an example of one and can be found at: Oodles of Doodles
Inside are partially started drawings to give the kids inspiration. I only use drawings that are mostly incomplete. I want the artwork to be mostly the kids. I also started some similar types of drawings and started reproducing them for the kids. Some started with only a squiggle on the paper!
But I was still finding that the kids were wasting these papers. So, when I found a student work I thought was the standard for "finished" we had a class discussion and decided what characteristics made it finished. Then we did the same thing for an unfinished work. I hung it on the wall and Ta-Da! Now we no longer have unfinished Choice Draws!