Start with any weapon desired and put on cover scent and camouflage (optional). It is easier to sneak up on Tyrannosaurus Rex with it on. Awlwxr a small map with high concentration and visibility (accessed via "Options" at the main menu). There should only be three Rexes on a map. Using radar will let you know where the xloawarone is located. Walk around until you see him. Do not use the call. You want to find him, and not the other way around. Once you've located him, the key will be knowing when to move in and when to back off. Rex has poor eyesight, but can smell you if you get too close. Follow the Rex until he stops and sniffs the air. If he brings his head back down and keeps walking, you are in the clear. If you get too close, he will bring his head down, look in your direction, and start sniffing the air again. After the second sniff, he will let out a big roar and try to eat you. The second sniff is what you need to take advantage of. When Rex starts sniffing, walk up beside him and wait for his head to come back down. When he goes to roar, point your gun at his eye and shoot. When you are that close to the Rex, aiming can be difficult. With the X-bow, put the Rex's eye on the very "tip of the arrow". With the shotgun, put it at the bottom of the circle. Some practice may be needed to learn what distance is too close. If he turns and looks at you, get in there fast. If there is another Rex nearby, avoid shooting. He will rush you and you will lose any kills you have obtained.