Mix light and heavy Mechs in your groups. Have a few of heavy Mechs in the group, then set the lighter Mechs to guard the heavier Mechs, then just select the heavy Mechs to control. With this you can control certain Mechs while others which are set in guard mode will attack the enemy automatically without orders. This is useful for base assaults. While your lighter Mechs keep the enemy busy, you can take your bigger Mechs and destroy your main objective or hit the enemies hard from behind. Keep in mind that in guard mode the Mechs often swarm and circle the enemy and hit it from all angles. Again, set the lighter or faster Mechs to guard the larger or slower Mechs. Deselect the Mechs in guard mode, then select the heavier or slower Mechs and control those only. The Mechs in guard mode will do everything, from attack to evade, automatically.