A tactical fundamental is the perimeter.
Whenever you are stopped, or if you are about to be engaged by a superior force, you need to find cover and concealment and circle the wagons to cover 360 degrees around you. By doing so, small units have been able to hold out against large forces for surprisingly long periods of time.
The leader of the group typically controls the unit from the middle of the perimeter. From here he tries to maintain a 360 degree situational awareness of what is going on. Each guy on the perimeter can only watch his own sector so he cannot worry about what is going on behind him. The leader has to see the “big picture” and make decisions.
If he has them, the leader will keep a communications element with him and a reaction force (AKA “The Reserve”).
If under attack, the leader has to keep the perimeter as intact as possible. If a member goes down, the position will either have to be filled by a member of the reserve element or the perimeter has to be reduced to maintain 360 degrees of fire. The leader makes sure that ammunition, water and equipment is distributed around the perimeter. If a member is knocked out, his ammo and equipment needs to be given to the remaining members who need it.
The leader has to be aware that the enemy my be launching “probing attacks” to judge the strength of his position, or to scout out gaps.
Once the leader determines that the enemies main attack is under way he will try to bolster that area of the perimeter with the reserve.