Please see Rick & Kathy's Website Cooking In Cast Iron
They have alot of tips on taking care of cast iron and a great video if you'd rather watch tips. Below I have listed a few but check out the website when you get a chance to, it is really worth it.
1. Use your pans and use them a lot. If your pan has just been seasoned fresh (as opposed to factory pre-seasoned) or re-seasoned it will probably be a shade of brown, BUT it should be completely black within a year if it is used frequently. There's very little that cannot be cooked in cast iron. Rethink the kinds of pans you use. If you normally cook something in the oven on a cookie sheet, it might cook just as well in the skillet. On the stovetop, skillets can be used for much more than frying, but obviously, they're good for that, too. Breads and desserts cook well in cast iron skillets, too.
2.Keep them handy, either on the stove top or in the oven when not in use.
3. Since cast iron distributes heat so well, under normal situations, you don't need to turn a stove burner above a "medium" heat. Always let the pan heat as the burner heats or let the pan heat in the oven as the oven heats. Don't put a cold pan on a hot surface or a hot pan in cold water. Either has the potential to crack or warp the pan.
4. Check out Rick & Kathy's website...