First off, don't every practice breath holds in the water by yourself. You could pass out and die. Always have a buddy to spot you.
Breathing up for a breath hold should be somewhat deeper than just normal everyday breathing, but should be slow and relaxed. On the inhale you should fill you lungs over a period of several seconds, maybe 5 ,6, or ,7, or whatever feels natural and relaxed for you. Don't try to get a maximum lung full, just enough to comfortably fill you up. You don't want it to feel like w
tweakbox appvalley https://vlc.onl/ ork. On the exhale just let the natural elasticity of your rib cage force the air out - just let the air "fall" out, then at the end just do a little squeeze of your abdomen to force the last part out. But again, in a relaxed way. You don't need to strain or force ALL of the air out. The key to breathe up is relaxed breathing to fill and empty your lungs with no straining. So you should be doing a breath cycle evey 10 or 15 seconds. Do this relaxed deep breathing for a few minutes before starting a breath hold. Look at forums on Deeperblue. Learn about "belly" breathing - the preferred way to breath - fiil your "belly" first (bottom of lungs) follwed by the upper lungs/rib cage.