Others have given great suggestions. I will add this: Have fun. Smile at what you see and just enjoy the dive. This will help you do better with air consumption.
You might want to smile in your mind and not necessarily in your mask. Sometimes smiling in your mask causes a leak LOL.
Diver0001 beat me to the punch. If conditions allow, in a group, dive higher in the water column than your group. The suggestions for yoga breathing are very good. If you achieve yoga breathing (and thus Zen), you won't even believe the further extent to which you are going to enjoy your dives over the course of your lifetime. As maxbottomdiver said, learning to breathe in that way improves not only your diving but day to day life. I find it particularly effective during potential road rage moments.
