I was pretty bad at stealth in the game, so one thing that made this trophy much simpler for me was realizing you can stealth kill surrendering enemies. When an enemy crouches down to yield, crouch behind them and as long as you have a dagger in your inventory the stealth kill option will come up.
If you play primarily with a bow like I did I found the most effective way to incentivize enemies to surrender was a chest shot. Headshots are usually fatal and leg shots rarely got the result I was looking for.
Another note, stealth kills don't always register right away. I'd check my stats page in the player page and it wouldn't be registering the stealth kills, and then all of a sudden a bunch would register at once.