Each town (Lothering, Redcliffe, and Demerin) has job boards posted in front of their Chantries. You can also find jobs for the Mage's Collective from their Liaisons in Denerim and at Lake Calenhad. Redcliffe and Denerim also have the The Blackstone Irregulars that you can do jobs for. Finally, in Denerim at the tavern in the Market, you can jobs for less reputable people. Complete 15 of these quests for this achievement. Most are pretty simple and don't take nearly as long as the main story quests.