My list would include

Careful release of air
Planning your breaths
Learning to take very quick, deep breaths

People often emphasize abdominal breathing (drop your diaphram), but neglect the other areas that you can relax and expand. To get a really full breath, you need to open and relax all your muscles around your lungs. This means you will expand your ribcage (back breathing), lift your chest (not your shoulders), and drop your abdominal all in one. Knowing how to do it is difficult enough that it requires practice. Try thinking about each one, in turn, as you take and slowly release your breath. Then combine them. The hardest thing for me, is to keep my ribcage lifted and expanded after the air is gone. If you can keep it open, the next breath goes in very quickly and easily.

At any rate, breathing well is just hard to do, but very rewarding. If you have good air, you will be more on pitch too.

Claire