Note: This solution is solely on how to max stats. For getting all pet tricks and expressions, please use one of the other wonderful guides posted.
There is a very easy way to get max stats without grinding for numerous hours. While in-game, plug in a second controller and DON'T choose a gamer profile. When it asks 'Do you wish to continue?', say yes. Now on controller 2 (aka the henchman), go to the abilities, and discard every ability that the henchman has, you should have a lot of green EXP after you discard everything. Now have the henchman quit out. Then on controller 1, go to the abilities page, and you'll see that the hero now has all the EXP that the henchman discarded. Use the EXP on whatever you wish and then rinse and repeat. Should only take 20 minutes tops to max stats.