From left to right, articles are ranked by their importance to that particular WikiProject. From top to bottom, they're sorted by article quality, with the best on top.

The ripest fruit you can find will be the intersection of Stub articles (the lowest rated) and Top/High importance. That means they're important topics, but that the coverage is lacking.

Stub and Start articles of Mid, High, or Top importance are all good candidates.

You may also find something particularly relevant to your course that is rated "Low" importance. It may still be a good candidate (and may be rated as a "High" or even "Top" importance to another WikiProject).

Avoid Featured Articles and Good Articles, regardless of their importance. Editing these articles can be a bad experience both for new editors and for the editors who have worked to bring these articles up to a certain quality.