I'm pretty good with air. On a shallow dive of 15-20 meters, I can easily stay down for 80-90 minutes. My advice for getting the most out of your tank:
1. If you smoke, quit.
2. If you're out of shape, get in shape.
Those are the two big ones, I think. Also, take it easy the night before you dive. Being hungover is a way to burn through air.
For me, the biggest change in my air consumption came when I get my buoyancy down pat. I practice it a LOT. For example, if I'm not particularly enjoying a dive or part of a dive, I practice hovering just over the bottom using breathing only. I know exactly how much weight I need when I dive - whether I'm wearing a 3, 5, or 7mm suit or not wearing one at all. If you're overweight and have to compensate by inflating your BCD, you're creating drag - i.e., making yourself work harder.
Another big thing: Stop kicking. You're working the biggest muscles in your body and burning oxygen.