what is causing my armature to warp the model so badly when rotating it's arm, how can i fix this? i've just finished setting up an armature for my model, i used automatic weighting which may be the cause of the problem, but whenever i try to rotate the arms or legs of the model, it causes catastrophic effects on the model's proportions. 
if the solution has to do with manually painting the weights, is there a more precise way of editing the weights? i would like things to be symmetrical and that, instead of just doing it by eye.







i would rather the shoulder stay in place when raising the arm, instead of putting it halfway down the torso

thank you
Yes, your weight painting is off, you'll have to use envelopes (not the best solution) or manually adjust the weights, so that the upper arm does not effect the chest anymore.
Select the armature, then the guy. 
CRTL + TAB -> choose weight paint.
Use the brush tools to adjust your weights.