Snipeing is an art...
Its all about opportunities. A good sniper will know his surrounds, the entire map, and the quickest way to get from "A to B". The location you set up in is important like what every one said. Stay away from mosque and church towers, god hates snipers in his house. But anyways around these locations are prime spots for the s-mine you carry, for if you kill someone that's the first place they look for you. another thing is most people will be drawn toward that area so if you stay "near" the sniper pickup spot you will attract you competition. Okay now on to the three main points earlier. Know you surroundings... Y would u hide there if you can name no more than three in 30 seconds stay because its not an obvious spot, you want two things for your snipeing spots cover(from bullets and sight) and the ability to see. Secondly why would your enemy come near your location. if you are in an area with something valuable(a special kit, a spot to get a drop on your base, anything attractive like that) move, it will attract extra attention. Now you want to know the entire map, my favorite place for snipeing is at the airfield, you have a lot of plane campers well standing there. Another thing may be considered smaktardish is camping "over" spawns if you know where an enemy spawns take aim a shoot, but once if you miss dont shoo(and miss) again. Other good opportunity points are turrets, tank spawn and of course special kit spawns. A to B is well line up near b so you can see A and you have nice targets moving toward you.
Other tips...
1. Shoot once, you may shoot again if the target seems to of not "noticed you". stop after three and give the kit to someone else.
2. Use typical behavior to pick your spots.
3. Set as high of screen resolution as possible.
4. (havent done this) turn graphics down so plants dont load and you have clearer shots at opponents.
top o list with sniper is possible got 47 kills with sniper in a match. took two squads down with sniper who where advancing at me to win the match. so yeah i kinna know what im talking bout
sorry for long post if it bugs you.