Mark gave you some great advice. The one thing I can add is his advice about sauce. If you like yours thinner, keep the cover on while you cook. If you like it a bit thicker, leave the cover off (you will lose some liquid to evaporation).

Also, when you do add cornstarch to thicken a gravy, never do it while it's boiling, and always take it off the flame. Add the cornstarch mixture, stir briskly so that it mixes well, and then return it to the flame. Bring it slowly to a boil. At that time, if it's still not thick enough, take it off the flame, and repeat the steps until it's to your liking. It's hard to judge how much to add, it will just come with experience, and remember that you can always fix it by adding water to thin it out, or more cornstarch to thicken it. If your family is anything like mine, we can never get enough brown gravy, so I usually add a cup of bullion to my drippings.