Follow though is just that, "follow through". Basically it means, getting a good point of aim, good sight picture, smooth trigger pull, (this is where follow through comes in), after the trigger breaks getting back to your good sight picture as you recover from the recoil. Taking another good sight picture before you relax your position.
In coaching, I tell people, after the shot breaks get right back on target (good sight picture) as you were firing rapid fire and needed to break another shot.
Normally people shoot and want to "drop" the rifle/handgun to see where the shot went. What happens, subconsciously, you drop the rifle as soon as you break the shot. It takes a spit second, that movement causes the rifle to drop simply because unknowingly, you are dropping the rifle while the bullet is still in the barrel. Thats why you can tell if "follow though" isn't happening by seeing the shots break low.
If we practice proper follow though, as in any other aspect of shooting, we develop muscle memory. What happens if you practice the above (getting back on target after recoil as if you had to fire a follow up shot) we develop muscle memory where as we subconsciously force the sights back on target, and if we jump the gun (pardon the pun) and start the movement before the bullet has a chance to leave the barrel, we actually push the sights back on target instead of dropping low.