the main purpose of digging would be to get money fast, which would mean leveling is less important. if you only want money, then only dig, and let the levelling occur when it does.
if, however, that doesn't satisfy you, there are other options. a locked post titled "larkinor character guide" shows how to make digger/mage or digger/fighter combos (or if you're a subscriber, i believe it even has digger/thief and digger/robber). following those make it easy to fight monsters and dig inbetween, allowing levelling faster, but still making money from digging.
one other option i have found is, because a digger is suggested to have at least 8 IQ, so they will have enough mana to build magic weapons (to sell for profit), i found that if you just continue with IQ=lvl (all other points into luck) for low levels, you can still fight effectively with magic. and by lvl's 10-15 or so, you would either need to put points into quickness, or else increase your IQ (to lvl*1.5 or 2), and selectively fight monsters who are weaker to magic (some are very resistant) in order to continue fighting to lvl faster... otherwise, by that time, just concentrate on digging, and forget the fighting.
sorry this got to be so long. hope it helps.
--jason