One of the keys in generating sales referrals if asking your referrer to think in terms of pictures. Human beings think in terms of context, so if you can successfully generate a picture in the head of your referrer, you are more likely to get a good referral.
Wrong: "Do you know anyone that wants to buy a car at a good price?"
Correct: "Let me ask you about the people in your office. Do you think any of them might be interested in getting a car at a good price?"
When applied to the job search, try to get your referrer to think in terms of decision makers instead of general terms.
Wrong: Do you know anyone looking for someone to work? Is your company looking to hire?
Correct: Do you know anyone in the Marketing Department? What about HR? Is there someone you know who regularly hires?
Finally, make sure you take the referral into your own hands. If you were a salesperson, you wouldn't let your referrer try to sell your product, so why would you let a job referrer take your resume and try to sell you? If you want the referrer to help, have them call ahead or send an e-mail to the contact letting them know that you are calling.
And don't forget the thank you.