When swimming underwater, focus on the connection of the arm to the water. The catch is crucial to effective movement through the water.
Great stillshot of what your ideal freestyle looks like is to be found at 0:55!
Elements of a great freestyle:
Hip Rotation - Glide on your side for maximum stroke length and to really engage the latissimus dorsi. Those muscles are made for strong, long-term use.
Position the wrist below the elbow - Notice in the video that the swimmer’s wrist is always below his elbow. This “high elbow, early catch” position is critical in grabbing the most water.
Fingers down, elbow up “S” pull - Pull directly below your body line with your fingers pointing down.
Relaxed palm pull - Relax your hands so that all of your fingers are just touching. This provides a nice, large pulling surface with which you can connect with the water. Also, it will keep you from wasting energy trying to keep a “cupped” shape with your hands which only tightens your muscles.
Finish your stroke at the hip - Finish your pull past your hip. This is what is known as the push phase of your freestyle stroke. Some people are “pull dominant” (meaning they get more power from the first half of their stroke) while others are “push dominant” (that is, they get power from the back half of their stroke). Regardless of which category you fall into, finishing at the hip rounds out and balances your stroke. Accelerate through this phase of your stroke to make the most of it.
Yet another great video on stroke efficiency from GoSwim. Rather than interject my own comments, I will allow these videos to speak for themselves. The principles found herein can be applied to all four competitive strokes. Enjoy!