There are many ways of grinding, and AI3's have the wider variety of ways to grind (pretty sure I made a mistake somewhere in that sentence).
You can go for EM (end with 100hp), in which case you'll need heals (other decks use vampires). You can also go for speed grinding, in which case mono death is the fastest unupped (6 poison, 6 mummies, 4 bone dragons and 14 bone pillars, it's awesome), but it can be boring. Fun grinding can be slower, but my "fun" is in nova bows (I mean, every hand is different, and you can tweak the deck to have lots of useful combos)...
If you're afraid of getting bored, try looking for decks in the forum, the deck archive is huge
If you want EM grinding, the best should be something like 4 dragons, 6 cockactrices/frogs, 6 heals and 14 pillars (I haven't even made the image of the deck, but I can assure it'll at least have more than 90% against AI3)