Never take a risk. Never attack when there is any chance off ailure. Always separate the enemy. Always wait, if there is time. Use undead to separate them. Use terrain to separate them. Use organic elements of the environment. No direct contact in the first area, use secondary elements to slow and kill opposition. Be behind the enemy rather than in front of them. Set up a battle. Send in a significant force of expendables and watch them fight to see what they do.