Steady Hand, Great Scope 50
Hunt an animal with the Rifle that is at least 50 yards away while using the Scope (in Story Mode).
Location Chapter 4 - River Delta or any level with cheetahs in the trees. There will come a point where you can see with Hunter Sense a cheetah in the tree. Just back up as far as you can and scope in the little kitty and shoot it, the achievement should pop up. If not then you were too close.
Bow In Front of Me 50
Hunt 20 animals with the Crossbow (in Story Mode).
Location Chapter 5 - Grassland. You will come to a point where you enter a shack. Located inside the shack is a crossbow and some bolts. Basically use the crossbow from this point until the end of game and rack up 20 kills.
Adventure Over 100
Complete the Story Mode.
Simply beat all 11 Chapters in the game.