Ammo, Barrel, Sights/Optics, Trigger.

Ammo. Garbage in, garbage out.
Barrel. Crap barrels wont shoot no matter what you put in them.
Sights/Optics. You have to be able to see it to hit it.
Trigger. Get a Geiselle, JP, or an AR Gold. They aint cheap. Cry once.

Dont forget about the loose nut behind the scope. They need instruction as well. Remember even Gold Medal winners have coaches.