Just move with your squad, and practice with your weapon enough to be able to make the accurate shots that the other rifleman cant take. That, in essence, is a DM. Now, to do this, you need, as mentioned before, simple practice. However, practice, good as it is, is greatly aided with the installation of a tight bore barrel, a metal spring guide and bushings, a good shim job, and at least a 350 FPS spring, (With a good hop up). Just practice taking out small targets from far away, and your all set, as that is the job of a DM.