I noticed that I was using a lot more air at the beginning of the dive than at any other time. I figured that in the gear donning and entry period we are more task oriented and just busier than once we are 10 minutes into the actual dive. I have tried to focus on relaxing, not hurrying and getting ready sooner before getting into the water. This seems to help.
One other thing I found may contribute. I find my SAC, which my computer calculates every 20 seconds, would be high the first few minutes of a dive. Well, usually it was warm outside, 80s or 90s, and I was jumping into 40 to 60 degree water. The change in temp of my cylinder lowered the pressure until the cylinder was cooled down. I confirmed this by some dives in the Fall where the water and air were about the same temp, and did not see this high SAC at the beginning.
Terry