Quote from DeepThoughtAuction House Tutorial:
Search for other items of the same type as yours. Use the important stats as search critera: in this case 64 intelligence, 80 vitality, crit hit 7.
Look at the range of prices on items that are a little worse, near the same, and a little better than your item. Understand that the prices you see are *asking* prices and not prices people will necessarily be willing to pay.
Find a good price point, list your item, good luck.