Wikipedia Education Program/Handout: Article selection (Large Wikipedia)

Some indicators of a potentially good topic:

terms that are well established in the relevant discipline, but only weakly represented on Wikipedia
topics that are specific and narrow enough to be manageable, but broad enough that sufficient sources exist to write a solid, sizable article
"Stub" and "Start" class articles, which typically have only 1-2 paragraphs of information and are in need of expansion

These kinds of topics should generally be avoided:

topics covered in related articles, either as large subtopics or as different terms for the same or very similar topics. Before creating a new article, it's a good idea to spend some time searching related topics on Wikipedia to make sure the topic isn't already covered.
very broad topics (e.g. Law) or articles that are already of high quality on Wikipedia
topics that are highly controversial, e.g. Global Warming, Abortion, Scientology, etc. (Start a sub-article instead.)
topics only sparsely covered by literature
articles with titles that imply an essay-like approach, e.g. "The Effects That The Recent Sub-Prime Mortgage Crisis has had on the US and Global Economics" instead of "Subprime mortgage crisis"