In art school we used to do 'true' exercise photography by doing things like:

• Take n pictures of a single object, making sure that no two were the same (n was generally some large number like '100' or '250') - The exercise was designed to train yourself to begin to see the many ways it's possible to approach a subject...
• Find an object and take the exact same picture of it every hour for 24 hours (generally an inanimate object... Humans won't stay still for 24 hours! Lol) - The goal was to see how even something that doesn't move changes quite radically depending on what is going on around it.
• One of my professors used to hate zoom lenses so much that his requirement for letting us use them was that we had to submit a picture at every whole f-stop for every marked focal length on the lens before we could use it for assignments - His intent was to train us to know the capabilities and differences of each focal length so that the zoom functionality didn't become a crutch when composing shots.
• Take 100 pictures of objects that have a common characteristic (they're all buildings, they're all less than 1 inch wide, they're all blue, etc.) - The goal was to learn how to find interesting pictures 'hiding inside' everyday objects.
• Take 100 pictures from a perspective you wouldn't normally think to take pictures from (lying down, under water, upside down, cropped to 1x6, etc.)

As an aside, I went to art school long enough ago that we were doing all of this on film. Even though I bought in bulk, used B&W film, self-rolled my film canisters, self-developed, and most of the time we only had to turn in contact sheets of our work (thank God!), looking back it was still an incredibly expensive thing to be a photography student...