RIFLES: Generally, these men are going to be used to initiate the ambush and provide a steady dose of accurate fire, as well as conduct maneuvers on the enemy if the situation/plan calls for it.
MACHINE GUNS: These are great for delivering a high volume of accurate fires on an enemy position in order to keep the enemy down or take out a large unit with accurate and devastating enfilading fire.
SNIPER/DESIGNATED MARKSMAN RIFLES: These weapons can be effectively employed to take out covered targets or delivering a precise and single shot to take out HVTs that could assist the enemy in returning effective fire on your ambushing element. This could also be put in an offset position to pin down enemy elements attempting a flanking maneuver.
In addition to the above mentioned weapons, you may have a range of others that can be employed against the enemy to enhance your capabilities such as rockets, mortars, etc.