Read through this brochure on evaluating Wikipedia articles, especially pages 4-7. This will give you a good, brief overview of what to look for in other articles, and what other people will look for in your own.
Evaluate an existing Wikipedia article related to the class, and leave suggestions for improving it on the article's talk page.
A few questions to consider (don't feel limited to these):
Is everything in the article relevant to the article topic? Is there anything that distracted you?
Is any information out of date?
Is each fact referenced with an appropriate, reliable reference?
Is the article neutral? Are there any claims, or frames, that appear heavily biased toward a particular position?
Where does the information come from? Are these neutral sources? If biased, is that biased noted?
Are there viewpoints that are overrepresented, or underrepresented?
What's missing that could be added?
Check a few citations. Do the links work? Is there any close paraphrasing or plagiarism in the article?
