My dad explained to me once some basic concepts he learned in the Marines. The goal is to created an upside down triangle. Your guys want to be the V part and line on top of the V that make it an upside down Triangle is your enemy. You basically want to put your enemy in a cross fire, so your shooting at them at multiple angles, getting around their cover without coming in at too sharp of an angle so your not shooting your own men. The Machine gunners would give covering fire, keeping the Bad guys heads down while the riflemen would keep moving (cover, shoot, move, cover, shoot, move) to try to outflank the bad guy.
Then my dad would laughed and said, that is the theory. In Vietnam it usually did not work out that way.
I guess the short answer would be one member of the pair would try to pin the Bad guy down, while the other tries to move to a better firing position to shoot at the BG, and then take turns.