Don't get in the open when there is a sniper. You will be dead.
Don't think you can't be seen by a sniper because you're hiding in the grass. To keep the framerate up, the developers made it to where grass only appears when you are close to it. Therefore, a sniper can see you perfectly in the grass.
When sniping, don't forget that you are at risk. Someone could easily sneak up and kill you.
In steal the sample, place claymores by the your sample so when the other team comes to get it they will almost always die.
Also you can adjust where you would like to place your branch whips on a tree. So try to place them as low to the ground as you can that way they are much harder to notice, but have the same affect. To do this you just have to look towards the bottom of the tree (in case you didn't know).
I'm not sure what the problem is for you Dave527. Although, someone earlier asked about claymore mines. To lay them down hit black button and look at the ground. It should transform from a branch whip into a claymore. Try it, and tell me how it works.
My best advice is to always point the end of the weapon with the round hole AT the target always. My shoulder still hurts learning that little life lesson...
When people are sniping near a tree, tell your friend to make a branch whip, but fire your machine guns so he doesn't find out, then tell your friend to get out, then throw a grenade near the sniper. Its a guarrented death.
Use the WATER, if you take heavy fire and are near enough water to dive into.... go for it, it has saved my life many a time especially when you get caught in a fire fight and then i would usually pop up behind them and slot em in the back of the head!