Not an amazingly great exploit but an exploit that can save you a little bit of time. When you start the quest where you plant the flags over killsorrow fortress guys corpses grab a partner. Kill the guys and if possible try to time it with your partner to plant the flags at the same time. You will get double credit for the flag making you only have to kill 10 guys if you are trying to get it done quicker. Same applies for the next part of the chain where you plant the flag over the Ogre corpses.
P.S. - Will try to find the name of the exact quests.