Arrays are the meat of graphics. If you want to do anything to more than one thing you have to use arrays. Just like artists do gesture and contour drawings to warm up and practice, array manipulation is excellent practice. Here are a few things you should be able to do with arrays: reverse their order, count through them forwards and backwards, resize them, move the stored items around like a conveyor built, sort them, copy them to name a few. I hightly recommend The Euler Project, you'll need to use lots of arrays to solve the problems there.
// Processing JS:
// http://processingjs.org/