I Have not been able to find any information regarding proper meditation breathing techniques from Gnosticteachings.org or SAW. This is an extremely important topic because if we are not breathing proper we cannot meditate properly. It is not possible to go into the deeper states of meditation and relaxation if you are straining while trying to meditate. This has caused me heaps of trouble and frustration personally, and I see others asking questions about breathing with no answers.
Abdominal breathing, and chest breathing are great for certain pranayamas, but if we want to completely relax our nervous system and allow deep relaxation so that we may get more out of our meditations we need to learn Diaphragmatic Breathing.
In diaphragmatic breathing, one does not move the abdomen or the chest at all. This is done by expanding the ribcage only.
It is not complicated, and the link below explains it very well. Personally, this has helped me vastly. I hope it helps you too!