I had the Covergirl Foundation for a while, but hardly used it. The jar's glass was too thick and took up too much space, so I put it in a smaller jar and added a little something.
Once you have your foundation in its new container, put a few drops of Proactive Daily Oil Control. You can use anything else of course, but i had that in handy. Keep in mind that adding too much will change the consistancy of your makeup. I stirred it with a clean paper clip, but use what ever you like.