Swimming is the most technical sport. Improvements in technique can have a drastic performance improvement. Here are my top three drills.
One arm swimming. One of the most difficult things to do when trying to improve technique is to remember all the things that need to be done with your head, arms, elbow, legs etc. What I like about one arm swimming is that you can concentrate on one arm and do a proper catch and pull all the way back. You can actually watch the one arm the whole way while holding your breath for a couple of strokes. Keep the other arm in front for balance and remember to rotate to the opposite side although you may not actually breathe to that side. You often find that your left or right arm swimming is not as efficient as the other. This gives you an opportunity to work on it. Swim left arm one length of the pool and then switch.
Full catch up. One way to explain full catch up is to put together left arm swimming and right arm swimming together with full strokes of each side but never moving one arm at the same time as the other. One arm always waits in front while you complete the whole stroke with the other and return to the front. Push off the wall with both arms in front. Now do one full stroke with one arm and bring the arm all the way back to the front &,ldquo,catching up&,rdquo, to the other arm. Once both arms are in front momentarily switch and do one full stroke with the other arm. This type of swimming creates a little bit of a pause while you are bringing the arm all the way to the front yet not pulling with the other one. You may lose momentum. It will be important to work on your body position so that you can glide each pull and also kick to not lose all the momentum. This drill when done in combination with the one arm swimming allows you to build your technique.
Fist swimming. This drill is self-explanatory. You swim while creating a fist with your hands. What this does is force you to utilize your forearms to pull which is the proper way to pull and maintains a high elbow catch. If your fist swimming is substantially slower than your peers then make sure you look at how you are performing your catch and pull when swimming normal. On the other hand if your fist swimming is not that much slower or perhaps better than your peers you can feel more secure that your catch is proper.