Once you have an idea what you want to research, write the topic down in the form of a question.
How does home schooling affect social development? Do harsh sentencing laws reduce violent crime?
Unless your assignment is asking you to take a specific position (for instance, "Assisted suicide should be made legal.") it is important to leave your topic as a question. Most researchers start with an assumption, but understand that the information they find might lead them in a direction they hadn't thought of. This is actually one of the most exciting parts of research - finding out other perspectives and information.
Once you've written your question, underline the main concepts or ideas in your sentences:
How does home schooling affect social development? Do harsh sentencing laws reduce violent crime?
Leave out words that lead you to an assumption - like cause, reduce, affect, etc. as these often create false hits or biased search results.
Too Broad or Too Narrow?
A good rule of thumb is that you should have 2 or 3 underlined main concepts in a "good" research question.
Having only one main concept means your topic is too broad: Home schooling
Having more than three main concepts means there might not be much information on something so specific: How does home schooling affect the social development of girls in Massachusetts?