Before you search, try this short brainstorming exercise:
1. Make a list of all the words you can think of associated with your topic. Do this without evaluating what comes up or worrying about relevance, order, or spelling. Just list as many as you can.
2. Go back through the list and pick out the ten or so best matches--the ones that most closely match your ideas or the assignment.
3. Use these words as search terms. Try searching for two or three at a time, joining them with "OR," or searching for an exact phrase.
4. You can go back and repeat this process as much as necessary.
When you are just starting, try doing this with three or more different topics and see what you find.