here is a little advice to help those struggling through the levels. the first topic: What should I be doing at the vendor?
try and sell all items not need for money, which you can exchange for larger swords and better defense. I even sell traps and runes.
Start by uprgrading your warrior then the mage or archer, in the following way:
WARRIOR - longsword, metalhelmet, metalshield, ringofmobility
MAGE - meltalhelmet, both wand of fire and health
ARCHER - longbow, metalhelmet, metalshield
The mage and archer can wear full armour if you wish. Trade in items! a few archer grapes can be traded in for a longbow or helmet.