Sniper Rifles
In my opinion sniping can be split into two main categories, albeit with some overlap. The first involves finding a good spot and then proceeding to pick off anyone foolish enough to tray into your field of fire. The second and I believe the more realistic version requires regular relocation, the reason I believe it is more realistic is that a sniper is a highly trained individual and it is in his and his sides interest to keep him alive and racking up kills as much as possible. You chose a spot pick off a few targets an as soon as they realise where you are you relocate, preferably to somewhere where you can take out the enemy troops trying to sneak around behind where you were last.
Before you get to the stage where you can chose you need to do some homework. To snipe requires that you know as much about each map as possible, make mental notes of any position you see a sniper (friendly or otherwise) and experiment with new locations yourself. I still find new spots every so often on some maps that I have played less. Once you have found a god set of spots on a map make sure you study the fields of fire and know the directions enemy troops are most likely to come from so that you can anticipate them.
I would also suggest you try inspecting these positions from the opposing view. With a bit of luck you'll spot a few places where you are virtually impossible to see from the sniper spot. These are critical in two ways, firstly you'll have to keep your eyes on them at all times and secondly you may well need to use them in counter-sniper mode. Snipers make a very effective weapon against other snipers but only if you see them first, remember that it is part of your role to keep enemy snipers quiet as well as inflicting as much damage to the enemy in terms of men and morale.
Now we get on with the real task at hand, killing people without warning from a distance. Remember to always aim ahead slightly to combat lag, the amount is something you'll have to experiment with until you find a suitable leading distance. Crouching or better still lying down when ever possible reduces the sway making shots easier.
Keep back from windows as far as possible to make yourself harder to spot and avoid unnecessary movement as it is often that which gives away a sniper's position. Look with your eyes not the crosshair and stick to standard view rather than zoomed apart from when you see an enemy as it gives you a much wider view preventing you having to keep moving the scope around. Also try to find dark areas or areas with a pattern that your uniform blends in with, some of the best sniper spots are out in the open and require you to just lie on a pile of rubble and keep still to avoid being seen.
Now you can shoot and hide you are almost there, you merely have to get into position without dying and/or relocate safely. My only advice here is take it slow whenever possible, use team mates for backup, sprint when you have no cover and keep your eyes and ears open. Your rifle may be uber-accurate whilst scoped but when unzoomed you have no crosshair making hitting a target more luck than skill. Practice will see you being able to hit targets at close to medium range with some regularity but once you fire that first shot switch to your sidearm to finish them off. I find at medium range it's often more effective to stop crouch, zoom in, aim and then fire. With time you learn when each is more appropriate and will be able to perform either defence in an instant
Allied SMG wastes no time and sprints accross open ground to minimize the
time he is vulnerable