Actually, no qualifier is needed. The expression:
How to aim a [pistol/rifle/weapon/etc]
is perfectly natural (example). By default, when you instruct someone how to do something, it's assumed you are telling them how to do it correctly.
However, if you want to emphasize that there is a correct method and and an incorrect method you could say something like:
How to correctly aim [a weapon].
As SamBC mentions, you can substitute various synonyms for "correctly": properly, accurately, appropriately, effectively, etc. You can also suggest you're teaching a particular technique: quickly, smoothly, steadily, etc. Example:
How to safely and accurately aim and fire a fully automatic weapon.
Also, by default, when you "aim" a weapon it's assumed to be at some target. Otherwise you're not really aiming it, but rather just pointing it in some vague direction.
As an alternative, you can use the idiomatic expression "take aim", which is commonly associated with the action of aiming a weapon, rather than some metaphorical aim.
How to correctly take aim at your target (when firing a semiautomatic rifle).