Show, don't tell. Once you've got a working version of the program, evaluate again. Provide only the basic instructions necessary to proceed, and let users learn by doing. It should be possible for users to restart the exhibit and return to the previous step from any point in the program. The whole activity should last between 3-10 minutes.
Interactive exhibits work well when they have a clear beginning, middle and end.
Keep navigation simple and be consistent. If the Start Over button is in the lower left of the screen, make sure it is always in the same location. Keep text concise, but make it fun to read. Readability of text fonts is important. We try to keep ours at 14 point or larger.