Successful waterborne training isn't about swimming. It is about being comfortable in the water: whether finning, swimming, treading, or floating.
It is about minimizing energy expenditure and maximizing efficiency. It is about controlling the mind and emotion while you are fatigued, cramping, and cold. You will not be able to avoid these. Accept it.
Control panic, control your breathing.
Some keys:
(1) As Hillclimb said, use you lungs as another Buoyancy Compensator. Fill the lungs to max and use it to help keep the body afloat. I use a combo of scissor kicks and egg beater.
(2) Use smooth, gliding motion of the arms. Think of the arms as wings: keep the leading edge of the hands slightly tilted up as you sweep the arms back and forth. This motion can be used for propel forward and upwards (look at vids of penguins/seals as they swim). This is much more efficient than flapping your arms up and down and is much less fatiguing. There is only one time where short, jerky motions are acceptable.
(3) Learn to control panic. Accept getting water in nose and learn to control coughing when water enters past the epiglottis. Don't panic.
(4) Maximize ventilation times, i.e. use the time that the head is out of water for inhalation. Exhalation can come any time.
Those are my tips for now.
If you or anyone else are serious about committing to your paths, I'll share some more tidbits.
