Now for Fault.
The two blue X's together are sniping points for the SEALs. Go to either spot on the top platform and you'll be able to hit the far tunnel, the waterfall, and the entrance from the base of the falls. Just make sure someone is watching your back, because it's easy to get sneaked up on here.
The other blue X is another camping spot. Not the greatest, since you can get hit from the platforms and such, but it works if you have teammates with you.
For the first red X on the top left, go prone and corner-peek, and you should be able to get the jump on anyone trying to get in, just as long as there isn't grenades.
For the red X on the bottom, Just press against that wall, and you can cover the entrance pretty well. Just somewhere I prefer.
The final red X to the right, works just like the first red X - go prone and you should be able to get the drop on any rushers. It should give your teammates time to get to their positions or advance.