There are two schools of thought, on how and when to apply concealer; before or after the foundation. This school says after. When you apply concealer before the foundation, all you do is end up wiping it off when you do apply the foundation. Choose a concealer that is going to blend with the foundation. Usually if you stay within the same makeup line you will be able to buy foundation and concealer that will complement each other. It would be silly to end up using a concealer that once you apply it on top of the foundation, does not harmonize or blend in and just makes a mess  

And, keep to the same shade as the foundation. If you use a concealer that is a shade lighter, you end up highlighting what you are attempting to conceal. Some use a light face powder to dust your work into submission. Well, that could work, but what happens when the powder goes away, as it will during the day. You will still be left with your original artwork. You better be happy with it.  

Remember the three basic fundamentals of makeup, blend, enhance and be natural, and you can’t go wrong.