Other than increasing my fitness substantially, which is a long-term goal, are there any techniques from the Zen Zone to decrease the usage of air?? And how do you work out how much air is consumed??

I kind of figure that if i was fit then i'd use less air... but i'm not. Hence the question

Fin less.
Relax
smoke
buy a rebreather


How much air do you use?

I have been trying to reduce my consumption rate for a long time but I am stuck at about 20 surface LPM.

I reckon relaxing is the biggest one, well it was for me. I usually have a cold water SAC rate of between 15-18 LPM.

It is amazing how much muscular tension can make you expend more energy.

The two biggest things that helped me reduce my air consumption were being relaxed, and being neutrally bouyant.
Relaxation comes with time, being used to the underwater environment.
Buoyancy is something divers get told early on in training that they've mastered when in reality they haven't at all. Watching many divers out there - they finning all the time. They're probably not even aware they're doing it. It's a bit like constantly jogging on the spot. If you stop finning completely, you should maintain the depth you're at. If you don't, you're not neutrally buoyant. And if you're not neutrally buoyant, you'll be working all the time, and using up air to maintain depth. Being neutrally buoyant also helps you relax more. Resulting in less gas usage.

Another way to use less air is to be a girl. I'm not sure if having a sex change would help or not though.

Oh yeah. Good trim helps too.

Also spending a bit of time in the water before you descend. Especially if it was a hard swim to the anchor line. Get your breath back before you drop down. Also if you carry a snorkel try removing your mask and lie face down in the water using the snorkel to breath for about 5 minutes. This helps trigger the mammalian reflex and lowers you sac rate and heart rate.

Part of your answer will also come with knowing how long you've been diving. I know that when I started I could suck through a tank in record speed, because of a mixture of the above reasons, but also because I was constantly thinking about everything! With a few dives under the belt I started to relax a bit and it did improve.

Now, I'm not ballerina here, and I can still suck through a tank pretty quickly (and could do with improving fitness which I'm working on!), but I find that I will use more air on dives after a bit of a layoff, or when trying unfamiliar new equipment too. Once I have relaxed a bit again and remembered that it's not too hard after all I tend to improve. When I went to a drysuit I was all over the place again and sucking down that air like sherbert.

I used the get my breathing sorted at descend point technique, lying with face in water and a snorkel, and found that helped too. But as Flipper mentioned, getting my buoyancy sorted gave me the best overall result (and it's still not perfect by the way), so if you haven't maybe hook up with some of the people here about some practice dives to sort that, or get some decent training on it. Other than that the safety stop is actually a bloody good excuwse to work on buoyancy, at least for 3 minutes!

It'll come, but no magic cure that I have found...unfortunately