Too wet
Dry it slowly! Drying it quickly will lead to more crinkles and cracks than granny's feet. Be sure to dry leather at room temperature and in whatever shape you want it to end up in.
Too dry
Grab something moist and rub it in there. Choose a cream or conditioner made from natural ingredients to rejuvenate and keep your leather supple. Also, stick with light, clear options to avoid discoloration.
Too dirty
Keep it simple, a damp cloth will do wonders for dirt or mud stains. Stay away from soaps as they run the risk of drying your leather out. For more serious stains try a leather cleaner that won't lift the and remove the dye.