I utilize a parks and recreation pool located close to my home, since I work full time as well as living in the Pacific Northwest, which can always make the dive training somewhat more challenging. During the adult lap swim time gives me the opportunity to use the deep section for the static breath hold portion of my workout.
I personally feel that the workout done in full gear, sans wetsuit, prepares the mind to accomplish the task that I am setting before it, so I utilize my mask, fins and snorkel & weight belt for each workout. I must confess that the pool sometimes fluctuates in temperature by as much as 10 degrees, so I do wear my 2mm suit.
To mentally prepare myself, and to give myself a workout as well, I swim enough laps with my gear on to cover a distance of 2 miles. This also helps to train your leg muscles to adapt to kicking and gives a good cardiovascular vascular workout as well.
I usually do this in about 20-25 minutes, getting my heart rate up to my target heart rate for an efficient aerobic workout.
Once done, I go into a rest mode of just floating, trying to clear my mind for the next task of the shallow water static breath hold that I will be doing. With enough weight to hold me down on the bottom, I take 4 to 5 deep breath's and then drop to the bottom. I initially discovered that the first 2 or 3 tries can only get me a bottom time of about 45 seconds at most.
These initial attempts at breath holding begins to prepare the body for the longer attempts that I will be going for during my deep water workout at the other end of the pool.
Between each attempt, I give myself a good 3 - 4 minutes of rest to ensure that there is as little of a chance of SWB as possible. I have found that my mind slows down considerably during this stage of my workout, thus ensuring complete focus on the task at hand.
The main part then consists of moving to the deep end of the pool. I hang from the ladder and concentrate on slowing my heart rate down. I can't explain how I can do it, other than the idea of meditating on something that gives me a feeling of peace.
Once ready, I drop to the bottom of the pool, face down, and try to relax as much as possible. The first 3 attempts seem to only produce times in the range of 60 - 75 seconds.
After that, though, my times immediately become longer, in the range of 2 - 3 minutes, with the same 3-4 minutes of rest between each attempt. I log each time on a wrist slate for my training log on my computer.
This portion of training ranges in time of about 30-40 minutes.
I finally commence with the breath hold and swim underwater portion of my workout. This always seems the hardest part, but is also the most realistic simulation as well.
The goal here is to tuck dive to the bottom at the deep end, and then swim along the contour of the pool bottom until reaching the opposite end. I have found that this really helps to focus my efforts on efficient kicking and relaxation while moving.
5 - 6 times is my usual number of reps for this portion. By no means is this a scientific way of training, but it has served my individual needs for accomplishing my personal goals of freediving, a sport that truly brings me a sense of peace when participating in it.
Done 3-4 times a week, in conjunction with some light weight lifting and another aerobic exercise (Stair master, etc.) can bring one to a point of personal satisfaction in their pursuits of freediving.
