Use your skills

Before giving up on monsters, assuming you can't kill them because you're only
hitting them for a few points of damage per hit, try using the magic and skills
you've acquired while levelling up. You'd be surprised how much of a
difference a flaming sword makes while chopping down trees.

If the monsters still take several heal berries to kill, or if the amount of
time required to kill the monster is not what you would consider efficient, you
may just be underlevelled for the quest you're undertaking.
http://www.gamefaqs.com/computer/doswin/file/930711/43300