4 focal points I discovered while trying to swim better

Relax: easier said then done right.  It means relax whole body in water from fingers to toes!

Posture: achievable but if cant relax as above, render the stroke for show and inefficient and ineffective for the swimmer.

Breath easy: tendency to retain air in lungs when practicising a new movement, this is our body's natural response to prevent lack of oxygen.  Best leave this part till last when stroke posture is consistent and achievable at will  then work on breath.

Hydrodynamics: Despite proven theory on streamline posture, but with different body shapes, body buoyancy centre requires slight variation of effective streamline posture in water.  Mammals like otters, seals, sea lions, polar bears are great swimmers, but none of them practice a universal stroke technique to go as fast as they do in nature.  Their aquatic ability and efficiency is all instinct and feel for the water.  So it is better for humans to achieve personal streamline efficiency to adapt this animalistic approach coupled with technical knowledge to achieve the desired effect of swimming smooth like hot knife cutting through butter(in water).

Size of pool: depth of the water relative to distance swim, somehow requires slight adaptation of stroke technique to achieve efficiency.  This is especially obvious when swimming butterfly from deep end of the pool back towards the shallow end of the pool.  The pushback effect of the volume of water does not make my butterfly easier in shallow water, in fact my stroke suffer a drop in hydrodynamic efficacy and I always struggle to regain buoyancy swimming towards the wall at the shallow end of the pool.