Tactic, common in TS, FFA and Bomb mode games, where no autos are allowed: the player jumps and moves as much as possible, to make the player a harder target, as moving targets are very hard to hit. Then, to shoot exactly as the player is stopped, so that the shot is as accurate as possible. This is one of the hardest tactics to master in the whole game, as the player must keep moving a lot while tracking the target, which is probably also moving a lot.
Tactic, that is most prominent on TDM and CTF games, around a ridge in the map, or over the top of a wall, where autos are allowed: keeping as much of the player model hidden as possible (because autos are more likely to damage a large, yet moving target, than a small, but stationary one), the user stays in cover, peeps out, finds a target and fires. Usually this is used by less skilled players as it is easier, because the player does not need to count in the movement of himself as a factor. But, the main downside is the time it takes to see a target, which could by the time the sniper is able to shoot, either be in cover or firing at the sniper. Another danger when using this tactic is that other snipers can pin the player down while he is exposed.
Tactic, that is used as last resort or when the enemy is very close and best not aware of your presence. Successful use depends on many factors, with practice and swiftness being most important. The user moves or jumps as fast as possible towards the enemy to point blank range (often using jumping skills), pressing trigger without switching to the scope. Though the accuracy is very unreliable when not aiming through the scope, it does not play any role at such a close range. Due to the long reload time, this tactic is not adviseable against more than one opponent at the time.