I always tell my students to keep a sketchbook and draw or paint whatever they want in it.
I usually never tell my students to do something I don't do myself, so I have many types of sketchbooks filled with many random things I have drawn or painted over the years. Some things I like, others I don't, but that's how anything in life is right? It's just a good practice for an artist to keep making and creating as often as possible to maintain and foster their craft. I'll post a few pages of my sketchbook in the next few weeks..