Start with Oxford Art Online to locate information about an artist. Use the bibliography at the end of the article to identify books and articles about the artist. If you cannot find the artist, try Art Full Text for articles. If you are still not having any luck try searching for the artist in one of the newspaper databases. Finally, try the internet. Wikipedia is often good, (hope there are citations in the article) and many artists have their own web sites.
Start with Oxford Art Online to locate information about an artist. Use the bibliography at the end of the article to identify books and articles about the artist. If you are still having trouble, search the International Bibliography of Art, Bibiography of the History of Art, and JStor for articles. If you still cannot find anything, try Dictionary of Artists or Allgemeines Kunstler-Lexicon. This provide minimal information, but often have bibliographies that are useful. Even if you do not read German, you can usually find the bibliography, if there is one, in the Kunstler-Lexicon.
Overviews of Movements / Periods / National art / techniques
Oxford Art Online is the best place to go.
Describing a piece from the MU Museum of Art and Archaeology
You have to describe the physical properties of the piece and put it into a historical context.
Use Oxford Art Online to find information about its historical context.