I am a progression based teacher. Focusing on the fundamentals and then expanding to more difficult items. Practicing bad habits only makes them harder to change later down the line. Adults that are in good shape, have no option to increase speed and efficiency, except through technique improvement. Kids can become better by improving physical stamina if they have poor technique, but they are sacrificing their future speed through reinforcement of bad habits. Either way technique improvement is the solution.
How do we improve technique?
Mastering the little things is a necessity. I get laughed at all the time asking Adults and kids to float at the surface. Keeping the hands to heels at the surface. When they have a hard time keeping their body line strait and at the surface, they understand why I made them float. It exposes weaknesses of body position, which ultimately leads to slower, inefficient swimming. You must have constant attention to technique details to maximize what you are capable of achieving.
Technique tip 1: floating
Shoulders up and turned in, relaxed hands at the surface, head in line with the spine, eyes down, controlled core with a small LOWER back arch near the hips (I call this a hip lift), toes pointed, heels at the surface. Press the head and chest down, water level mid head, lift hips and feet, while staying relaxed.
Doing it properly is not as simple as it seems. Technique is the Solution.