I've found that the more creatures working on your side, the better your chance of winning the battles. This is becuase the tougher critters are less likely to target you if they have a dozen others breathing down their necks. To achieve this, have at least one cleric who memorizes nothing but animate deads. Also, have at least one mage with a wand of summoning creatures. For traveling in the outdoors, I camp immediately after entering a new area, and upon waking, cast all the animate dead spells I have (3 at the moment), which yields me an army of 18 skeletons. Late in Chapters 4 and 5, however there are some tough indoor battles. Again, rest before you go inside to refresh your spells. Creatures won't follow you through doorways, so you will have to cast them right when you enter. In combat situations, have the cleric and the mage (equipped with the wand of summoning) aim their first spells directly in front of any enemy archer, mage, or cleric to distract the damage. Repeat this immediately until all the enemies are surrounded,
and pull them back. Finally, you can have your fighters/thieves equipped
with bows starting picking off the enemies one by one while the
skeletons/wolves/hobgoblins/knolls nibble at their heels.