Use Terrain to Mask Movement – when moving units, you must strive to keep your enemy from spotting your units, or least strive to keep him from being able to place direct fire on them. Whenever possible place an obstacle between your moving units and the enemy.
Historical Example: the important point is to ensure the terrain feature you are using lies between you and the enemy as shown in these images. (from US ARMY TD Platoon field manual)
Technique: whenever possible keep terrain obstacles (woods, hills, etc.) between you and where you either know or suspect your enemy is located. When an obstacle is not available you can create one with smoke (if it’s available), then use that as if it is an intervening obstacle to mask your movement.
The goal is to maintain security and attempt to keep your movements hidden from the enemy... failing that, at least make your units tough to spot to keep them from taking fire.
Example 1: from my CMBN-MG BETA AAR versus c3k I maneuvered my reconnaissance assets as far forward as possible behind a ridgeline, then dismounted and moved forward on foot to spot the area ahead without risking their valuable halftrack.
Example 2: from my CMRT BETA AAR I plotted the movement of these infantry teams and ensured their movement was kept behind any rise in the ground I could find.