During the Tainted Blood mission in Ostargar, collect the three Vials of Darkspawn Blood but avoid collecting the Grey Warden Treaties. After you have the vials, talk to Duncan and choose the conversation option "We have the blood, but not the scrolls." The conversation will end and you'll get experience! You can repeat the conversation and get the experience each time -- you can do this all the way up to the level cap at 25 (if you are patient)! You can click through the conversation fairly quickly once you've done it a few times.