Watch the Anatomy & The Diaphragm online guitar lesson by Karan Andrea from Guitar Player Wanted: Vocals A Plus
The first concept is, again, a basic understanding of anatomy. Most of us are 'chest breathers' since normal speech doesn't require all that breath support. We just breathe in and out with our chest, and we're good.
Singing requires more deep breathing and deep breath support. Of course you know that your lungs handle the breathing part - there is a large muscle just beneath your lungs called the diaphragm. As you breathe in deeply, your diaphragm lowers and your ribcage expands to make space for the volume of air coming in. When you are breathing deeply and correctly, you can feel it from your tailbone, to your lungs, and your back. You keep your ribcage and back expanded and pull up and in from your groin. This supports your diaphragm, which regulates the air flow through your cords.
So a little trick that will make your deep breathing more efficient is to learn how to keep your back and ribcage expanded even as you exhale. Then when you have to inhale, you are simply 'grabbing a refill,' rather than making bigger, inefficient moves that will interfere with phrasing, timing, and support.