How to Swim the Freestyle

The head should be down with the eyes looking directly at the bottom of the pool. This position maximizes streamline and reduces drag.
The head depth should be such that some water travels over the swimmer's cap [for more information check out breathing during sprinting].
The top of the swimmer's buttocks should be at the same height as the top of the swimmer's head. Once again, minimizing drag.
The postural line between a swimmer's head and buttocks should be firm along the horizontal axis. Any deviations from the horizontal line will cause excess drag.

The head turn is independent of the shoulder turn. Rotating the entire body will result in excessive rotation.
Breathe out explosively as the head starts to turn to the side on the horizontal axis. Explosive breathing will allow a rapid inhalation and quick head return to the water.
Breathe in fast when the mouth is just clear and return to look at the pool bottom very quickly (before the recovery arm is vertical).
Time the turning action with the arm exit (the time of least effort). If one turns their head as their arm is propelling, the amount of force during the pull will theoretically be distributed to breathing as well and overall decrease.
Streamline should be maintained at all times.
The postural line between a swimmer's head, shoulders, and hips should be firm along the horizontal axis.

An overtaking stroke pattern in FREESTYLE should be avoided. This is commonly referred as catch-up stroke and stresses the shoulder and minimizes horizontal propulsion.
Body roll consists of the hips and shoulders rotating to ~45° to both sides. This reduces frontal resistance and positions the propelling arm closer to the mid-line.
The harder a swimmer kicks, the greater is the amount of resistance developed. Kicking should remain small and fast and deviate to each side in concert with the roll of the shoulders/hips.
In FREESTYLE, a high-elbow recovery will facilitate good body roll.
In the middle of the propulsive phase of FREESTYLE, a line from the recovering elbow through both shoulder points to the propelling arm elbow should be straight.

The shoulder should be fully extended forward.
The shoulder and upper arm should remain extended while the body rotates to lower the shoulder.
The upper arm should internally rotate while the elbow flexes to position the forearm/hand vertically.
Abduction of the upper arm commences as part of a continuous accelerated movement

This part of the arm stroke should feel increasingly faster and stronger as acceleration is developed.

The forearm/hand should rotate to be vertical while the upper arm medially rotates and remains stretched forward.
As the upper arm abducts, the shoulder and hip should be at the deepest point of body roll.
As the upper arm adducts, the shoulder and hip should have rotated upward.
The finish-position should be completed as the recovering arm begins to enter the water [see Force Potential of the Early Vertical Forearm].

This part of the arm stroke should feel the strongest and fastest part of the total-arm movement. It marks the end of propulsive acceleration.
The adducted elbow should be as far back as possible alongside the swimmer.
The forearm and hand should be vertical and pressing directly backward.
The next movement after achieving the arm's end position should be the elbow being raised out of the water to initiate the arm's exit.
The hand and forearm should "round-out" as they exit the water.

Initiate by first lifting the elbow out of the water.
Recover forward along a direct line.
Emphasize an elbow-lift in midrecovery.
Time the recovery with the propulsive arm's action.
Enter fully forward, flat hand, finger tips first, in front of or wider than the shoulder.