I've had the same two diplomats running around making deals with people and accepting alliances, etc etc. Their routine/skills never seem to increase, they are both still on "0", or as Med 2 says "A turnip has more influence". If I take a city and leave the enemy's army in ruins I try to use my Diplomat to convince them to be vassels or give me money but I can never close the deal because my diplomats skill sucks so bad, so wtf? I just have to end up wiping them out or calling a truce.

Same goes for merchants and priests, whats an easy way to increase their skill?