Pistol Guide

Pistols are your average, basic, lower middle class weapon. They are slightly more versatile than Sniper Rifles because Snipers are ineffective at short range, but they lack the speed, range and power of an Assault Rifle. You can use Pistols at short to mid range, don't even think about long range. You will die. I promise. Even so, don't underestimate the Pistol. They do have their uses for the discreet player.

Close-Quarters Combat
Open fire. Marksman is your friend. Pistols don't overheat too quickly, so an entire "clip" should not be necessary.

Mid-Range Combat
Take cover and fire either between enemy shots, or whenever you can see them but they can't see you. Discretion is the better part of valor here, because most of the time the only reason to use a Pistol is because you are a class that can only wear Light Armor and your only weapon option is Pistol (i.e. Adept. Sentinel, and in the early game, Vanguard.)

Tips For Any Combat
Pistols do not overheat quickly, and therefore don't lose accuracy as quickly as other weapons. Don't be afraid to open a clip on someone who really deserves it. (Not recommended for krogans or other shotgun wielding enemies.) Pistols can also draw enemies out for a Sniper to kill faster.