improve down time

90% of diving is mental.

Totally agree. When I think of my happy place and get nice and calm my down time spikes.

Z

Amphibian a 3:00 min breath hold is very good. My best isn't much better then that.  I think I am a better diver in the ocean then when I am training. The improvements I made in diving came slowly over time.  I never dove deeper then what felt comfortable at the time.  When I started to make an effort to improve my diving I decided to focus on technique rather then breath hold.  At the time I thought about o2/co2 tables much like bluekayak does.  I figured If I was a more efficient diver I could dive for the same length of time, but I would be able to do more and it would be much safer.  I focused on fin swimming technique, eliminating unnecessary movements, streamlining my body posture, and perfecting the duck dive.   Later I changed my mind about o2/co2 tables and briefly worked on them as well.  I never practice breath holds underwater because it is not safe and you will get the exact same benefit when doing breath hold work on dry land.

I use to hyperventilate.  On a dive trip to San Benitos a woman showed me how to belly breath (yoga style).  She pushed her belly out, which lowers the diaphragm and creates much more space in the lungs to hold air.  I stopped hyperventilating and started belly breathing.  I had about the same breath holds, but I think this is a safer technique.  Since then my breath holds have gotten better.  Give it a try it may work for you as well.  I feel naked without my dive watch.  If I don't spend at least the same amount of time on the surface that I spent on the bottom then my breath holds rapidly drop off.  After a few dives they are 1/4 as long as they could be.  For safety I spend twice as long on the surface as I did underwater before I make my next dive. 

For me relaxation is very important.  I try to get to the point where I feel like I could fall asleep before I make a dive.  I am more comfortable floating on the ocean's surface then anywhere else.

I dive for fun.  I am not the best diver out there, my brother's breath holds are almost 2 times as long as mine.  I don't get competitive with him or my friends who are excellent divers about depth or breath holds.  We just dive to a depth that is fun and some times it is pretty shallow.

We have a guy at underwater hockey who is an excellent diver.  I asked him how he got to be so good and he said that one year he dove every weekend that was safe enough to dive.  I did the same thing the next year and saw a huge improvement in my diving. So like the guys have said before me "there is no better training for diving then diving". Underwater hockey helps too.  The guys who play at our club in sebastopol have very efficient fin swimming technique.  Hockey is probably better for improving recovery time then increasing breath holds, but it dose increase your breath holds and all the guys who play regularly have good breath holds (over 1:00 at depth).  If you can't play hockey then swimming with fins will improve your fin stroke.  IT will make you a more efficient diver so that you conserve your air and move farther with each stroke. 

Terry Mass' book Freedive! is a good book to start out with.  Manual on freediving by Palazari is a great book, but like you said it is very technical and only really worth buying once you feel like you have gotten everything you can get out of Terry Mass' book.   
     
our freedive instructor told us that o2/co2 tables not only lengthen the time you are comfortable while holding your breath, but also increases the amount of time you can hold your breath before you black out.  I don't know the physiological effects of tables on your body.  Tables are a very popular way to train for competitive freediving.  To me it makes sense that tables would increase the amount of time you can hold your breath before you blackout.  There are guys who are holding their breath for 7-10 minuets.  I doubt they were doing that without blacking out and only being uncomfortable at the beginning of their training.  After training they are able to hold their breath that long.   

In preparation for my freedive class with David Laird, I started reading the Freedive book. After learning to breath with my belly, I improved my breathe holding from 1 minute max to 2 minutes 45 seconds in just a few days, only practicing 3-4 times per session. I never knew it would make such a big difference, but it did. I also found that looking at watch increased my urge to breath much earlier. Now I just close my eyes and listen to my ipod to relax. I know I can reach 3 minutes with some more practice, but if I could stay under water for just 1 minute while hunting for rockcod I'm happy. I think a bigger challenge is learning how to go deep. I've never gone deeper than 12 feet.