Let them know who may be contacting them, and briefly outline the key elements you would like them to respond to. That way, your references will be able to respond with relevant information.
Keep your references up to speed on your job search and its results. By communicating what's going on with you and your job search, you're using your references to the fullest capacity.
It's appropriate to ask references to call you back and let you know how the reference check went. This will shed light on how you were perceived during the interview. You may also get a sense of what the key issues the employer is interested in about the job you're applying for.