Claymores, bouncing bettys, and proximity mines will come in handy if there are limited paths to your position. While Decoy Grenades will help to quickly confuse your enemy if they think they have the jump on you.
The added ammo will come in handy and allow you to stay away from your support classes longer. However, you will need to take special care in remaining undetected, by passing over the Nanoweave Health benefits, combined with the weakened shield of the infiltrator, you will be very susceptible to damage.
Cloaking Devices (special ability, default key is "F"):Hunter: Default cloaking device, most snipers will take this. Be sure to max this ability as soon as you are able. This will allow you to stay cloaked while you line up a shot. A helpful tactic to remember is: Cloak. Track the target. Steady scope and line up the shot. Decloak and fire ONLY if you are positive you are going to terminate the mark. Cloak, and return to safe zone while recharging. Remember, if you fire multiple rounds into an area too quickly, and without making a kill, the chances of your location being compromised become increasingly higher.
Depending on your range, you'll want to try and stay at the rifle's max range as well. Take a bolt-action type rifle only if you are confident in your aim. Also purchase a 12x zoomed scope for more accuracy at long distances. The 10-round semi auto rifles have less damage, but allow you to rectify an otherwise missed shot. Most have the ability to kill quickly, requiring only 2 headshots. These shots can be placed often times before stationary targets can react fast enough to find cover.
Another key statistic to be aware of is bullet velocity. Lower velocity requires you to "dope the scope" more, meaning that the windage, or elevation of the targeting recticle will have to be aimed higher than the actual target when placing long range shots. Each faction has a "Big Gun" specifically for Infiltrators, boasting the highest velocity available compared to other long range rifles. An example would be the NC EM4 LongShot.
Comes with a shorter range than the bolt-action, but they are either semi-auto or full auto, which allows you to take quicker shots at your enemy. I do not them recommend for the sniper role, as you're more likely to give away your position, since you'll put more rounds out at a faster rate. Scout rifles also deal less damage per round in comparison to sniper rifles.
Personally I enjoy using the Laser Sight, but really any of the attachments will do. The pistol is your 'oh no' moment. Swap quickly and unleash some hell. Don't forget to use your special ability if you haven't yet!
Try not to use the flashlight attachment, since as a sniper, the last thing you want to do is give your position away with it.