Keep it manageable and be flexible. If you start doing more research and not finding enough sources that support your thesis, you may need to adjust your topic.
A topic will be very difficult to research if it is too broad or narrow. One way to narrow a broad topic such as "the environment" is to limit your topic. Some common ways to limit a topic are:
Example: What environmental issues are most important in the Southwestern United States?
Example: How does the environment fit into the Navajo world view?
Example: What are the most prominent environmental issues of the last 10 years?
Example: How does environmental awareness effect business practices today?
Example: What are the effects of air pollution on senior citizens?
Remember that a topic may be too difficult to research if it is too:
Example: What sources of pollution affect the Genesee County water supply?
Example: How can the environment contribute to the culture, politics and society of the Western United States?
Putting your topic in the form of a question will help you focus on what type of information you want to collect.
If you have any difficulties or questions with focusing your topic, discuss the topic with your instructor, or with a librarian.