Techniques
I use a few different techniques. I don't think that lung volume has as much to do with bottom time as some people think: certainly it helps for deep equalization(Mayol didn't have big lungs-he was holding his breath for 4 minutes at 150' in experiments). Between dives, I spend at least 3 minutes breathing very deeply-inhale for 4 to to 6 heartbeats, hold gently for 3 or 4 heartbeats, and exhale for around 4 beats. When I'm ready to dive, I inhale for 4 beats and exhale without control, meaning that I let the breath out under it's own power. I do this about 5 times. Then I do the same thing again for 3 more reps, except I exhale forcefully through pursed lips. For the final breath I will exhale as deeply as possible, and turn on my side and spit out my snorkel to get "clean" air. My static breath hold was 4:30 until I tried the exhaling without restraint method. It instantly and consistently jumped to 5:30, so I use it all the time now. I have started to use the packing technique that is described by Eric Fattah in this website for stretching, and pre-dive. Packing has helped with equalization at depth: 6 "packs" before the dive seem to help.Any more than that (pre-dive) seems to negate itself, bottom-time-wise. Cheers, Erik