The best advice I can give in these situations is don't do what the game has to offer as fast as you can. You're going to run in to that boredom a lot faster if you just blow through what the game has for you to play. What I found to keep me interested is I practice at roles I haven't had as a main in the past. Granted, it takes me longer to max out a job than most people, but my playing experience has had longer legs than others as well.

Also, and I know this is going to seem weird for an mmo, but there are people playing the game at the same time as you. Just start a conversation in shout and have some fun talking to other people instead of just running through the dungeons as fast as possible.