Inhale Statics
If you don't have a buddy you can do 'dry statics' on the couch/ bed/ floor. Don't even think about doing it in a pool with out someone, trained in freediving, standing right next to you- and life guards DON'T count.
OK, no that the legal disclaimer is out of the way, you can start by lying on the floor and doing a couple of minutes of yoga breath- exhale twice the length of the inhale while breathing through the stomach. Take one final breath, inhaling through stomach and then chest. When you pack in as much air as you can, swallow- this relieves pressure on the throat. Close your eyes and dream away.
When you start to feel a contraction, a small spasam in your gut that signals the urge to breath, start counting them. You should be able to handle at least 5 contractions on your first attempt.
Exhale, and then start to breath normal again for a few minutes. Start your yoga breath up again for another 2 minutes and repeat.
You will find that each time you do this you can hold your breath a little longer and tolerate more contractions. I would suggest doing this at least 3-4 times per session. Do 2-3 sessions a week, with time off in between, and you should be able to hit 3 minutes pretty easily.
If you try this and want to do more I can give you more details later on. A couple of things will make this easier. First, don't try to hold your breath after eating dinner, wait at least 2-4 hours before your statics- digestion concentrates too much blood in the gut and your times will be short. Second, try and do this in a cool place as you will heat up once the contractions start.
As you can tell this will take some time to do. When I was practicing statics every day I needed between 45-50 minutes a day to set aside for them. Now I do other things instead.
Exhale Statics
If your looking to improve your breath hold for SUCBA diving I think Exhale Statics are the way to go. They take a LOT less time and will really build up your confidence in an O.O.A. emergency.
Start out the same way, slow yoga breathing, but on the last exhale try and force out as much air as you can. Then, hold it for as long as you can. Don't expect to go much past 20-30 seconds on the first try- and never do this in a pool even if you have a buddy. You can do a series of 6-8 in no time at all. I have been able to build up to a 2 minute exhale static on a good day.
The reason I like these for scuba divng is because I rig my gear in a DIR fashion- meaning I donate my primary from my mouth. I, now, KNOW that I can hand off my regulator after a full exhale and still have plenty of air left in my system to take care of my buddy first and then think about going for my back-up. Even if you don't donate your primary, it's still nice to know you can handle having your regulator ripped out and have lots of time to deal with the situation before you get out of breath.
There are lots of other things to try, like regimented 02 and C02 tables that you swithc off on every other day, but this should be enough to get you going.
Just make sure you ALWAYS have a buddy anytime you try to do any breath holding in the water- and swimming pools have proven to be the most dangerous place of all. Doing dry statics while lying on the floor insure that you can't fall down if you push yourself too far.
Jon