Begin by exploring topics. Art topics can be related to medium; artist; style/movement; time and place; subject. A few topic examples are listed below, but there are many, many more great topics that you can think of yourself.
Time and Place
Encyclopedias and videos provide good background for exploring your topic.
Now that you know a bit about your topic, think of questions that you would like to answer. An excellent way to do this is to combine two or three ideas from the categories in the [Topic] box: medium; artist; style/movement; time and place; subject.