Life's best tips normally come from a friend, so when one handed a new book to me the other day quoting that it changed his swimming dramatically and for the best, I dived into it pretty quick. The book is called Total Immersion by Terry Laughlin and it's good. Simplifies the way to swim, explaining it in easy steps and hammering it home to you that you don't have to blast it down the ruddy swimming pool as hard and fast as you can. The concept of making your body as looooong as possible certainly made me change my shit style pretty quick. Of course it introduces more bad days but at least it's for the better.
Here's another great article on Triathlon Europe 'The Seven Keys To Freestyle Swimming'