You need to have a reasonable understanding of the nitrate cycle, here is a quick guide.
Fish produce waste very similar to us, this contains ammonia. Ammonia is then converted to nitrite by a bacteria known as Nitrosomonas. The Nitrite is then converted into nitrate by another bacteria called Nitrobacter. The final piece of the cycle where the nitrates are consumed by plants and algae and of cause your regular water changes.
The first and most important thing is regular small water changes. As a guide about 10% change weekly in a aquarium with a high biological load, highly stocked aquarium or high nitrates in the first place. If your aquarium as a small bio load and low nitrates it is recommended to do a 25% change every month to help replace depleted trace elements. This really is common knowledge and should be part of your reef keeping maintenance.
Using the correct amount of live rock is important as this is your natural filtration, and to go with this you need a good amount of flow so that your live rock and it's small filtering inhabitants can filter and work there de-nitrifying effects on your water. Flow should be a minimum of 24 times turn over off the total volume of your aquarium, bear this in mind though when positioning low flow loving corals.
Using the correct amount of sand, many argue too much will create what is known as a "nitrate factory" A Deep sand bed can cause problems if not full of de-nitrifying bacteria, this can take time to mature, it is recommended not to use sand, using a light misting, enough to cover the surface for aesthetic pleasure.
I find that if using sand at any depth, to not disturb it. Using a Syphon and vacuuming the substrate in my opinion shouldn't be done. This removes the de-niyryfying bacteria and releases nitrates. After employing this method, i have found reduced levels of nitrates.
Stocking correctly and slowly, By over stocking you are asking for trouble, i suppose you can keep on top with very regular water changes but what is the point could you live in a 3 by 2 cubicle? Taking it slowly is not only easier on the pocket it also allows the de-nitrifying bacteria time to cope with the biological load. Like a good wine, it matures with time.
Over feeding can contribute to high nitrates especially on newly set up aquariums. If the food is not getting consumed then there will be a bigger biological load on the aquarium.