Shoot when the sun is behind you (dosn't really work on this though)
Know the terrain, for example at long range look and try to memorize what everything looks like, and know when there is a change in the landscape. That bumb could be a sniper!!!
Line up your shot twice at least
when moving move with caution and away from the infintry as thats most likley where the other sniper is shooting.
Use the terrain to your advantage, for example hills, shade as said earlier, creators, Ect.
EDIT: Analize the movments of your opponents, look to see whether there traveling in squads, by themselves, this can give you clues to big troop movments and have you end up with some kills
Check your maps to see whether your team mates are nearby this may make you more likley to get shot