brshooter, this is one of the most common plaints of new divers -- you are not alone!
If you think about it, gas you take down with you is like the gas in the tank of your car. If you want to get further on a tankful, you have to be more efficient. In a car, that means not mashing on the accelerator and then mashing on the brake, and not running at high speed when you don't have to.
Diving is amazingly similar. In essence, the more you move, the more oxygen you need to support the muscle activity. So, to stretch your tank, move less! How?
First of all, get weighted properly, so it's easy for you to become neutral and remain horizontal. If you aren't neutral, you have to kick up (or down) all the time to stay at the same depth. That's wasted movement, and wasted gas. If you're out of balance, say tilted feet down (most common), then every kick you do drives you upward. To compensate, you have to stay negative. Therefore, a part of every kick is simply wasted energy, which is wasted gas. If you can hover horizontal without much movement of your fins, you're becoming efficient.
Streamline your gear -- Minimize what's hanging off you, and weight yourself properly so you don't have any more gas in your BC than you absolutely need. That makes your propulsion more efficent, because you aren't kicking against unnecessary drag.
Keep your hands together, so you don't swim with them. Paddling with your hands is very inefficient and wastes gas.
Swim slowly! Diving isn't a race, and there aren't any prizes for covering the most ground. Lots of underwater life depends on camouflage for survival, and you won't spot those creatures unless you take your time and search with care. A small flutter-type kick from the ankles will buy you all the propulsion you need in calm water, and will conserve your gas.
And finally, keep diving. The more confident, comfortable and relaxed you become underwater, the slower and more rhythmic your breathing can be, and the more efficiently you will use the gas in your tank.
But overall, don't feel bad or guilty about sucking a tank down when you're new. We all did it to a greater or lesser extent. It WILL get better, and it will get better faster if you improve your technique.
