Use a cream concealer that matches your foundation. If your skin is very oily, use an oil free liquid but build your coverage and let dry completely between layers. Then set with translucent powder.
Hope this helps!
Try Make Up For Ever Full Cover Concealer -- it's the best I have ever used for blemishes, discolorations, etc. The tube lasts for ages (my own is still about 90% full despite owning it for nearly a year), because so little product is needed. It has a thick, dry consistency that really gives it staying power, and it's waterproof! http://www.sephora.com/browse/product.jhtml?id=P15