The better your trim, buoyancy, and finning technique, the better your air consumption will inevitably be.
Every bit of excessive movement- be it hand-swimming, erroneous finning, constantly having to reach up to dump air from your BCD, etc- requires energy, which in turn means you will breathe quicker. If you can, try to focus on only making deliberate movements. Work on developing a good frog kick, and treat every dive as an opportunity to consciously monitor and practice both your finning, horizontal trim, and buoyancy.
Above the surface, any sort of routine cardiovascular exercise should help over time.
Like any other skill, practice makes perfect. Not to mention, as you spend more time in the water, you will also inherently become more comfortable, which in turn will help your breathing rate as well. Good luck!