To start, you will need to start unlocking the different levels of takedowns available within the Perks page. There are several degrees to the perk line, allowing you to sneak up and take down specific ranks of enemies. If you're going for high-ethanol yields with outposts early, you'll actually want to try and sneak around and take all the enemies out so they don't raise the alarm to the others or actually call for reinforcements. The goal is to get up behind or close to them before they're fully notified of your presence and then press the
in to execute them. Or, if you're from above them, do the same while falling towards them for another execution.
If you do this after you've returned from the northern reaches of Hope County, you can actually get a perk called Eden's Touch that allows you to loot the individuals you've executed this way too.