Come up with a topic that interests you... and can keep you interested while you research and write. You should want to learn more about this topic.
If you cannot think of a topic or cannot decide on just one, there are databases that can help.
Come up with synonyms and similar terms to match your topic
Don't get too specific - It is easier to narrow down your results than it is to expand them.
Use * to search for different versions of the same word (truncation)
Use " " (quotation marks) to search for specific phrases