Charge your dot. Try to charge your rifle as much as possible before making a hit-- A good charged rifle is more powerful.
Aim for the head on heavier classes. This may be hard when they are in motion, but always try to get a headshot on a stationary player. The likes of killing him are higher than a lower shot.
Hide your dot! Enemies avoid walking into a sniper dot (if they're smart enough..) so try to hide your dot on walls where they cannot see it, on tall crates, in the water, etc.. you get the point.
Strafe as much as possible! A stand still sniper is most likely a dead sniper. Try strafing left and right while going against snipers. Moving snipers are hard to get.
Dodge bullets by jumping and ducking. When going against a sniper with good aim, try jumping and ducking a couple times while out in the open. It will make you a harder target. Just don't let go of your charging dot while in mid air.
Do not stay out in the open. When charging your dot, try hiding behind a wall. Also try to strafe behind a wall after you make a shot-- if you miss a targeted sniper, he might get you after you make your shot.
Remember: You cannot snipe without both of your feet on the ground. Try to stay away from walls with small edges behind them that would make you jump up. You cannot snipe while swimming, try getting on a floor if you want to snipe in the water.
Change your sniping spots. While you are in a sniper war do not keep returning to the same spot after you are sniped. Most enemy snipers are good at recognizing your strategy if you stay in one place. Same goes if you snipe someone. Run across the battlements to leave the enemy in question.
Learn your opponents strategy. Everyone has their own way of sniping. Learn who your going against and what type of techniques they use.
Never go up close to thin walls when in a sniper war. There is a bug that makes you visible through thin walls if you stand too close.
Do not walk into a dot. No matter if you are an LPB or not, a wall sniper gets the shot off first most of the time. If you are behind a wall and you see a dot waiting on that wall for you change your spot and get the sniper by surprise.
Recognize the classes you are shooting. You should always aim for snipers first since they can kill you the easiest. Then go for the lighter classes, then the heavy. If you want frags and don't want to be fragged, make your decision on who to sniper wisely.
Aim low at ducking classes. When a class is ducking, do not aim for their head; you will most likely hit the wall behind them. Aim for their chest or legs. You'll hit them, but it's hard to get a head shot.
Be aware of your surroundings. Know what classes your team has and most importantly know what classes the other team has. If they have medics and spies, you know that you will be their main target. There are many people who play just to 'hunt the snipers' so take note of enemies (excluding snipers) who will be bothering you the whole game; know when they are coming and where they are coming from; play defensively against them.
Be cautious against heavier classes. If a soldier is coming your way. Hide by a respawn door (if accessible), get a shot off at him and run. If he sticks around, try to get more quick shots while staying near your door. He has more health/armor than you and two quick shots from him can kill you instantly. Play smart when going against soldiers, HW's, etc.
Use your grenades! If you are being chased, throw a grenade at the guy chasing you. Make sure to time your grenade right so that when you throw it you make a direct hit.
Communicate! While on the sniper deck, you see what's coming and where. Warn your defense of incoming offense.
Be a team player. If there is a sentry that is hard to get by any other offensive class and is in a sniper's range, help your team out and get rid of it for them.