There are generally two types of snipers in DoD:S. The Defensive Sniper and the Assault Sniper.
The Defensive Sniper will focus on defending positions and just staying behind the front lines. Aim at paths that enemies would possibly pass through and you can get kills easily. Beware of counter-snipers measure like enemy snipers, rockets and grenades.
The Assault Sniper is perhaps one of the most difficult classes to master. Generally they follow other soldiers and go to the front line and help eliminate enemy personnel (especially enemy MG/Snipers) in areas that are hard to notice. As the Sniper Rifle is not designed for close quarter combat, one may find it difficult to counter automatic gunners at close or mid-range. You may have to practice how to shoot without using the scope with your sniper rifle and you need to learn how to aim with precision with both handguns.
It is possible to increase your rate of fire as a sniper by employing the quick-switch technique. Simply change your weapon from your sniper rifle to any one of your sidearms the moment you release the shot. This reduces the time it takes to animate loading the next round. Quick-switching also lets you start unscoped with your sniper rifle so that you can observe the battle field again after every shot. You can do this by either tapping Q twice very quickly after every shot, or by pressing 2-1 or 3-1 very quickly.
For handgun techniques, since the M1911 and the P38 both have a quick reload time and have a semi-automatic function, it is advisable to click and fire as fast as you can and reload quickly. The M1911 and P38's rate of fire are both dependant on the speed on which the player can click his/her mouse and thus can potentially fire very quickly (Even faster than the MP40). Although you only have 7-8 rounds on your pistol, having a quick finger can let you win a one on one fight against enemy smgs in close quarters as is it only takes 3-4 rounds to kill your opponent.