Cletus can be found at the question mark just northwest of Trevor's house in Sandy Shores. He'll ask you to go hunting with him, so follow him to the balcony and he'll ask you to shoot three satellite dishes. These are pretty big and are hard to miss, so look in the general direction of the red markers on your mini-map and shoot each one once to knock them over.
With that out of the way, he'll say there's some more hunting to do, so drive to the next spot and get into position. Cletus wants you to shoot the tires of three moving vehicles, which shouldn't prove too difficult, as the vehicles on the nearby road seem to move slower than normal. Remember that you need to hit the actual tire and not the rim.
Once you have gotten three, follow Cletus to one more spot, where he will tell you to kill three coyotes. There should be a pack of them nearby, but once you shoot the first one, the rest will start running away. You might get lucky and get one more before they get behind an object, but if you wait long enough, they should move back into range to their original spot. When three have been killed, the mission will be over.