It is generally recommended that when you first use your newly seasoned cookware that you cook something with a lot of fat, like bacon or hamburger. This will help soak that oil in and build up that protective layer that separates the metal from the meal. Some people will go so far as to suggest that you cook up a really fatty batch of hamburger and throw them away. If you've seasoned the pan right, you won't need to do this.
From this point onward you care for your cast iron by what you choose to cook. Fatty and/or oily foods will keep your cookware in great shape. However, acidic foods like tomato sauces or vinegary solutions will breakdown the oily coating and expose the raw metal. If you do cook things high in acid you will need to make sure you clean the cookware thoroughly and that you coat it in oil before you store it. Also, if you plan on using your cast iron for baking you will need to make sure you oil it well before you bake. Remember that cooking spray is the best friend your cast iron cookware will ever have.
Well cared for, the cast iron cookware will out last you. When you buy a new piece plan on which family member you will leave it to in your will. There are cast iron pans that have been in my family for 150 years.