your breathing is very important, set a regular breathing pattern of full inhales and exhales, and hold your breath only for a short period while releasing your shot. try to avoid holding your breath for more than 6 secounds
if firing from a stress possition, make sure you get your round of quickly, the longer you weapon is shouldered the faster your arms begin to turn to jello. shaking can also be decreased by ensuring the rifle is pulled firmly into the shoulder. maintaining a possitive grip of the weapon helps lower fatigue and make your shots far more accurate. try using sand bags when available and work on proper firing possitions, stance and weapon grip,
also as a side note, gripping the weapon further back (i.e the mag housing) causes your rifle to kick up more than usual. this sucks when you need to get off 2 or three shots durring those 10 secound exsposher serials. rember the c7 has a tendency to climb up and to the right of the target, its best to grip the weapon properly. also if using the mag housing as a grip be sure to keep your thumb off the ejection port, i accidently put my thum over the ejection port and got a painfull little burn as well as a bolt-partialy forward stoppage, not fun on a 30 secound serial!!!
hope these smalll tips help
cheers