To get more experience points earlier in the game, as soon as you leave Lothering, go to the city of Denerim. Once there, you will find a building named "Wonders of Thedas". Go inside it and purchase the Archivist's Belt. As long as it is equipped, you will get an experience point boost for everything in your Codex. Books will increase from 50 experience points to 75 experience points.