There are two different aspects of a guns accuracy. Where accuracy means impacting the same point repeatedly. One being the mechanics of the firearm itself and the other being the ability of the shooter.

Firstly here are some things that effect the mechanical accuracy of a gun:

• depth and consistency of rifling
• twist rate and it's compatibility with your selected ammunition weight
• barrel deflection from attached equipment (hand guards that touch the barrel for instance)
• bolt to chamber lock up
• ammunition quality and loading specs

Regardless of the human influences these things effect how tightly a gun will group.

On the human side here's what changes accuracy (alone) and is almost always the culprit of supposedly inaccurate guns.

• consistently aligning the sights with the intended target in the same way every time
• holding the sights in proper alignment throughout the trigger press
• pressing the trigger until the trigger breaks without shifting the proper sight alignment

Now there are some things on the mechanical side that can make properly doing the human things difficult.

• heavy or gritty triggers can make it hard to press smoothly without disturbing alignment
• a short sight radius or hard to see sights make consistent alignment difficult

Often times people will write off a gun as inaccurate because they aren't comfortable with it or can't manage it. Most guns are as accurate as a human is possible of shooting. But there are firearms capable of tighter groups than others.

If you're associating accuracy with the ability to strike a designated spot with consistency (shooting out the bull's eye) then you take the above listed factors and add:

• aligning the sights or optics with the guns bore axis (making sure the sights and barrel point at the same place)
• knowing the trajectory of the round as it relates to target distance (knowing how much bullet drop there will be at say... 100 yards)