I just came back and want to join a guild. I have done every lev85 quests and find myself unable to earn guild rep points. Any other way than instance and pvp? :/

Have you checked to see if you were weekly capped? Press J then highlight the exp bar.

Get an illustrious tabard. And make sure you're not capped. Grind dungeons...weee.....Takes a minimum of a month or more to hit exalted and that's if you're hitting your cap each week.

 

-----signature-----