Hi there. The best way to bring down your nitrates is with water changes. How much and how often do you usually do them?
What are your feeding patterns like? You may be able to cut down on feeding a little and/or make sure all of the food is eaten and if not, take it out.
There are different plants you can add to your refugium that'll 'soak' up the nitrates. I'm putting this site here just for some examples...
http://www.aquacon.com/vip.html
Do you have bio-balls? If so I would get rid of them (slowly though) and replace them with live rock. For an immediate decrease I would suggest the water change.