-Certain Bosses are difficult as soon as combat begins. They will start casting spells to hold, charm, or fear your party members. If you encounter a real nasty Boss who does not attack until they have a conversation with you, attack them before they start talking. If you weaken them before combat, they are much easier to defeat.
-When you have a low level party, have two clerics or druids to be effective. Send one cleric into a zone that you know has a pack of monsters, after casting Sanctuary on himself. The monsters cannot harm him, but they will all focus on him. Next. Have the Druid drops an Entangle on the pack of monsters. After that, have the party use with missile fire to kill the helpless creatures. This will not work against enemies that have ranged attacks. It is effective against low level mobs, such as packs of wolves and spiders.
-Summoned creatures (such as the skeletons from the Animate Dead spell) can be used to great advantage. Summon them near an opponent, then run your main characters away until you are no longer within sight of the battle. The opponents will stop fighting sincee they can no longer see your characters. However, your summoned creatures will still fight the enemy.