Kara Lynn Joyce swam for the USA at the 2004, 2008 and 2012 Olympics winning 4 Silver Medals. In this video, Kara presents 6 focus points for someone wanting to improve their swimming. Although, this video is over 50 minutes long, it is worth watching.
Always bear in mind, as Kara points out, "listening to your coach is the most important thing you can do". However, it is interesting looking at what such great swimmers focus on.