Not such a good choice
Articles that are "not such a good choice" for newcomers usually involve factors such as a lack of appropriate research material, highly controversial topics that may be well developed already, broad subjects or topics for which it is difficult to demonstrate notability.
- You probably shouldn't try to completely overhaul articles on very broad topics (e.g., Law).
- You should probably avoid trying to improve articles on topics that are highly controversial (e.g., Global Warming, Abortion, Scientology, etc.). You may be more successful starting a sub-article on the topic instead.
- Don't work on an article that is already of high quality on Wikipedia, unless you discuss a specific plan for improving it with other editors beforehand.
- Avoid working on something only sparsely covered by literature. Wikipedia articles cite secondary literature sources, so it is important that you have enough sources to provide a neutral point of view and be verifiable.
- Don't start 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). These type of titles, and most likely the content too, may not be appropriate for an encyclopedia.