If you stand just behind the tail rotor gearbox and look at the bottom of the tail boom, you can see the entire line of rivets along the bottom. As you walk alongside the tailboom during preflight, you should be looking to make sure the rest of the rivets are present.
Keeping in mind that the tailcone is a monocoque structure (there is no frame inside it) the structural rigidity depends on no dents. Think of a beer or soda can: they're pretty strong until they are dented at which point they can be easily crushed. You should make sure there are no dents anywhere on the tailcone. Common causes are hangar rash, but less common causes I have see are main rotor strikes on the tailcone!
Check the strobe and antennas by grabbing them and gently giving them a wiggle to make sure they are firmly attached. Don't shake them so hard that you cause damage!
The job of the attach bolts is to connect the tail cone to the frame. On this exterior picture, you can see the bolt side going through the frame, and through the doublers. On the inside there is a nut and a pal nut. You should check that there is no cracking of the tailcone around the mounts, likewise no cracking of the steel frame, and that the nuts are all present, with pal nuts, and that torque stripe is applied and not broken.