I've been working on improving my strokes. I also work on holding my breath, which has gotten to 3:06.19.
Thought I'd share the (free) resources that I used in addition to advices from collegiate swimmer, coach, triathlon competitor and one PJ.
Youtube has gotten more and more self-taught material ranging from proper Japanese pronunciation to swimming lesson.
The few that I use (all copy and paste):
Combat side stroke and 50m underwater swim
youtube.com/watch?v=4lUHudMN1TU
youtube.com/watch?v=6CM4vCf5rJA
youtube.com/watch?v=wSxdkuyIYW4
Arm recovery drills and tips
youtube.com/watch?v=IQJtcu5ZP84
youtube.com/watch?v=i-NE8_1OG3w
Total immersion/triathlon swimming technique
youtube.com/watch?v=KOun77ezffk
youtube.com/user/tiswim
Eggbeater & drownproofing
youtube.com/watch?v=lJpDiLynBp8
youtube.com/watch?v=Zf-3UTGppv4 (ignore the music)
Also this thread
http://www.professionalsoldiers.com/...ead.php?t=1318
Note that none of these are substitute for hard work & never-quit attitude. They are just ways to train smarter. As strokes get more efficient, there's less fatigue, longer swim range, and so on.