My starter project when teaching Photoshop tends to be this Mondrian Project because it teaches students the basic tools while allowing them to be creative. I have them focus on the Brush tool, Paint bucket and Color Picker to keep it simple. The first tool I show them is the SHIFT/Click combo that allows Photoshop to create a straight line. It goes, click on area you want the line to begin and then hit SHIFT and CLICK together where you would like the line to end. This always wows them! I also keep the project so they can only use primary colors with a focus on right angles.