do cows but instead of letting your merc do the killing, you should do it
in the end, it's much faster than letting your merc kill em all
after that do baal runs (when he's around 70ish) so you yourself can lvl as well
EDIT: oh yea, make sure you grab a shaftstop when at cows and of course, life leech gear (vamp gaze)- these items help a LOT