Apart from the obvious Enhanced experience shrines, there are other ways to speed up your levelling. I managed to reach 50 in the last Rift dungeon, without having to clear any dungeon that I really didn't have to.
More important than the weapons which give bonus XP per kill are armours which give you an XP award every time you get hit. Yes, that's right, you learn something every time someone smacks you on the head. Just imagine how much more XP you will be getting in boss fights or long fights against, say, replicating blobs.
Finally, clearing all monsters/treasures (buy keys if you don't have at least 3 before leaving town) and traps also awards a significant bonus. If you are about to leave a level and you haven't won the Killed all monsters award, then you've missed something. Unopened chests show up in the map, so it's impossible to miss them (unless you haven't thoroughly explored). You will need an item with the Reveal Hidden ability to help you with trap detection.