The unfortunate part of being a Warrior/Monk, when it comes to Positional Tactics, is that you really can't do all that much once battle has begun. You will be stuck in one place, fighting head-to-head with your enemy and there's really not much you can do about the other approaching enemies. However, that does not mean you should completely ignore strategy. First of all, you still have the option of getting an advantageous position before the actual battle starts. And second, you can still help your group members help you. Below are the three most common examples of ambushes I have run into.
A typical example. You (the blue square), a second Warrior/Monk and a Priest (both green) against two enemies (red) in a completely open environment - no trees or walls to interfere.
This would be the "wrong" way to handle the problem. As you can see, both enemies would be fighting against you now, giving the Priest a hard time healing you. At this point, I would suggest you made a small run clockwise around the enemy you were targeting (the top one) and the Warrior/Monk. The lower enemy would attempt to follow you all the way around, although at a slower pace.
Once you complete your run, have the Priest stand next to you as illustrated above. The enemy will now be locked in place (its movement pattern is illustrated with a brighter red) unable to reach you. At this point you could concentrate on taking out the top enemy without worrying about your pursuer. Be sure to tell the Priest what you have in mind - it's rare that anyone considers these things unprovoked.
Another typical situation when hunting in the Woodlands. You (blue), a second Warrior/Monk (green) and two enemies (red). Note that there is a tree in the middle of the battlefield (grey). Since you don't have a Priest in your group, the last thing you want is to fight two enemies at once.
This would be an extremely unfortunate outcome. Should this happen, instruct your partner to lure the other enemy around the tree, and then come back and position himself next to the tree…
… Like so. This way the enemy on the right would be caught behind the tree, completely cut off from the action. You could then proceed to kill the enemy on the right whenever you were done with the first one. Do remember that enemies have a tendency to cast spells when they're stuck, beag puinsein (poison) being one of the most common. Be sure to carry a few Personaca Deums with you if neither of you are Monks.
For the final example, here's a typical example of what I run into when money-hunting in the crypt. You (blue) against two enemies (red) both on the other side of a wall. This is one of the times when you should try to think about your position before you charge into the battle.
This is a perfect example of what happens when you don't think before you act. At this point you'd be very lucky to regain a good position without running away first. With two enemies hitting you at once, you'll be out of action before long, even if they are "weak".
However, with a little more consideration, you could produce this scenario instead. Obviously the enemy is completely incapable of reaching you so you can easily sit tight and take out one at a time. As in Example 2, remember to watch out for beag puinsein… it can easily turn the tide of battle if you aren't prepared.