I'm teaching myself freestyle, and my main source of information has been Fitness Swimming by Emmett Hines. I haven't followed his way exactly--for instance, I've never done vertical kicking, which is the first exercise in the book, for lack of access to deep water--but I've obsessively practiced kicking across the pool on my back and sides in fins with stationary arms (no flotation devices), and learning how to rotate around my spine while keeping my head more or less stationary. I don't yet have a snorkel (just bought one, waiting for it to arrive), so I haven't done much practice while facing the bottom of the pool.
My only current short-term goal is to be able to reliably swim straight lines across the pool in any position--prone, supine, or with either side down--in fins, and without using my arms for propulsion. I can easily swim across on my back or on either side, but I can't reliably do straight lines. When I reach the end of the lane, I'm often at a corner of it rather than the center. One problem is that my goggles tend to fog up so badly that I can't gauge my position by looking at the ceiling--but then, if my technique is really good, should I even need to use the ceiling? (I just bought antifog spray, too. We'll see how it works.)
Should I wait until I can swim a straight line all day long in any position without using my arms before I start learning to use them?
