Arrow to the Knee!:
This can easily be one of the first achievements you get after the tutorial. After acquiring the predator bow, make sure to set Low Draw Weight and the Carbon Impact Tip. This tactic will work in many areas, but the first area after getting the bow is easy. Once the door opens, go stealth, and try to sneak up to an enemy. Now put your crosshairs onto his knee. Without aiming down the sights, just quickly pull RT, hopefully wounding the enemy and not killing them. There may be some trial and error here, but just make sure to keep at a good distance and not to draw the bow too much.
Improviser:
Easily done during Mission 1, after acquiring the predator bow. After getting the bow, the first area will have a lot of grouped enemies as well as explosive canisters. The key is to try and use stealth, and find at least 2 enemies near a barrel, then shoot it killing both.
