This is not a difficult achievement, and will almost certainly come naturally during the game.
If you want to check it off ASAP though just to get it out of the way:
The easiest way to kill enemies by indirect means is to hit them into thorns or purple water. Very early on you'll collect your first proper weapon, and once you have it you can assign it to an attack button. I recommend
You'll see a lot of these horrible little pink slugs crawling around the place as you play through the opening sections. Walk up to one which is quite near thorns / purple water, and press
to launch them skyward. You can then immediately jump and hit them again to bat them across the screen a little way.
All of these enemies respawn over time, so don't worry about missing too much.
There are a few which are climbing up and down walls with thorns beneath them. They make an easy target! One upwards strike will knock them off the wall and hopefully to their death.
The achievement tracker keeps an accurate record of this.