Overkill is a common error early adventurers make. They make have gotten their hand on a nice sword, or magical ability, or even an artifact, and they go ALL OUT against a monster upon first sighting one. This is unnecessary. Just like with humans, small but deep wounds in the appropriate locations are enough to take out most living creatures, and just like with humans monsters often call for allies to help them when they are in distress. Use only as much power as you need to in order to end the fight, because if you overexert yourself then the second or third monster to arrive will make quick work of you and your party.
Eyes, nose, belly, mouth, and groin are all usually very susceptible to piercing attacks. Any area that you see energy accumulating at is often a good point to strike, as disrupting the energy will often cause blowback.
Strike and then retreat, bleeding out is a very effective way to take down most living beings.
Please be aware the above advice does NOT apply to constructs or demons. Unfortunately you DO need to use overkill in such situations, if at all possible.
-The Adventurers Guide to the Continent