The amount of air you need to breathe in a minute is set by the amount of carbon dioxide you generate. You can use efficient or inefficient breathing strategies (slow breaths with larger volumes are more efficient that rapid, shallow breaths) but the total gas you need can't drop below the minimum required to clear your CO2.
So the best way to reduce gas consumption is to reduce CO2 production, which means minimizing muscle activity. Efficient divers can stay longer on a given amount of gas. How do you become efficient?
First off, get close to correctly weighted. Do a formal weight check at the beginning or end of the dive (a search will give you a bunch of posts describing how to do this). Once you know what the total amount of weight you need is, figure out how to distribute it so that you can float in a horizontal position. Most weight-integrated BCs, in cold water, will put too much weight low on the diver's body, and obligate a feet-down position. When you are feet down, every kick drives you up and away from the bottom. In order not to ascend, you have to keep yourself negative. So a good part of every kick is completely wasted energy, used to keep you EXACTLY WHERE YOU ARE. When you are horizontal, every kick drives you forward, so you can do a lot less kicking.
Similarly, getting nicely balanced allows you to dive without using your hands. Waving your hands and arms in the water uses a lot of muscle, but accomplishes very little. Clasping your hands in front of you or under your body keeps them still, and reduces gas consumption.
Another way to reduce muscle activity is to SLOW DOWN. Diving is a meandering sport (unless you are spearfishing), and you see far more life when you move slowly. Camouflage is a major method for survival for marine animals, and if you move quickly, you'll overlook the clever critters. Slowing down will allow you to use a "kick and glide" technique, which will also give you a frequent buoyancy check (if you sink or rise during the "glide" part, you know if you're negative or positive, and can adjust your buoyancy accordingly).
And the last thing is that your minimum safe consumption is somewhat set by your size. A 6'4" muscular man is always going to use more gas than I do (I'm 5'4" and far from muscular!). There is no shame at all in a higher gas consumption rate, as long as you have done what you can in technique to minimize it. At that point, you just get bigger tanks
