Car leather maintenance is similar to maintaining the quality of your own skin, because that is what leather is: skin. Of course, the easiest way to prevent car leather maintenance is to cover the leather with a quality seat cover. However, this defeats the purpose of purchasing those beautiful leather seats in the first place. Get into the habit of taking a clean damp cloth with you. It can easily be kept in a zip-lock bag. Using a damp cloth, always wipe the leather off after using it. This prevents dirt and sweat from being ground into the leather between conditioner applications.
For more info, see A Guide to Car Leather Cleaning