new car care (interior, exterior)

What should be done to a new car to insure that it will stay in good condition? My car has been waxed, and the dealer cleaned the inside. Should I use a leather protectant right away, or is it okay to wait until the leather needs to be cleaned?

Also, I got some off odd black gunk on my jacket and then on my Sand leather seats. I bought some ArmorAll leather cleaner/protectant wipes and cleaned the stuff off. Is that stuff safe? It is okay to use it on just part of the leather seat without using it on the whole seat or will I end up with mismatched seat color later on?

Thanks,
Rourke