Tips
Depending upon what character you are and what weapon you are carrying, usually you can't carry nades. You can carry with NO ADDITIONAL WEIGHT. smoke nades. They work great to confuse other snipers in the area. Throw them in one direction, the enemy snipers will always watch the smoke for movement, then you can sneak into position and start sniping.
Also if you are using weaker sniper rifles, aim at the hips. By shooting the enemy in the hips this slows them down greatly. It gives you plenty of time to line up the next shot on their head or whereever. Usually newer snipers need to use this tactic. Once you get good, take head shots.
Once you have killed a few guys move to a near by location and watch the area you were just sniping in, also do this from round to round. You can usually trick someone twice. If you kill someone from the same spot twice, move, before the third time they will get you.
Get the Ghillie suits.