I am 360 gamer.
Anyways. I can try suggest you to find spot to train (Run around and let zombies chase you then turn around quickly and shoot then turn back and run. That is way you get points more and save ammo rather than waste on single zombie. Use common sense of course)
Since buried released on PS3 and PC, lot of small areas will be harder to train in higher rounds since non-stop spawns is everywhere so camp is something best option.
Try look up on youtube videos, it will help you get idea.
For random players, it really depend on how much luck you get to be with really good players. Just be friend with players who are good at zombies.