The cross-training routine that was previously posted on this thread had a variety of advice. Although quite a few people have mentioned to me that they prefer to swim, and don't really want to lift weights. That's understandable, but attempting to compromise I suggest these 4 critical exercises, 3xweek. This could take as little as 15 minutes, but will have significant impact on your swimming base times.
Ankle flexibility is crucial, as this is the anchor on your ship. Even if you don't improve power or strength, having your ankles flexible will reduce the drag and improve body position. So, I recommend a minimum of 6 minutes (3x per week), on the bike with your toes pointed. This is primarily to warm up the ankles as well as training the range of motion.
Don't be discouraged if you can't do this next stretch right away. When I started 8 years ago I couldn't get my knees off the ground, and my SDK was ineffective. Just have patience, and after several months you should notice a gradual improvement. Not everyone is gifted with natural mobility in the ankles, but the good news is this can be earned. Try and hold the stretch for 3x20 seconds.
Moving up the body line, core stability is critical for maintaining the right trajectory while swimming. Be sure to bring the elbow all the way around the knee, and tighten the core as you go through the motion. Pick a weight that enables you to do 3x12 reps on both sides.
This last exercise is great for your core, but I've noticed it is also really good for the upper body, especially the catch phase of the stroke, as well as engaging the lats on the horizontal axis. Again, 3x12 reps, and these four exercises can be made into a short mini-routine that most aspiring swimmers should at least consider.
So I finally have my video on FLOSWIMMING here it is
100 free SCM - 51.60 which converts to 46.02 SCY