What is the most effective way to improve the efficiency of swimming strokes?

By applying "hydrodynamic".

Hydrodynamics is a branch of material science that deals with the movement of liquids and the powers following up on solid bodies submerged in liquids and in movement in respect to them. Liquid hydrodynamics assumes a part in a swimmer's general execution, in light of the fact that the powers delivered in and by water can either increment or decrease a swimmer's speed.

it´s related to his charming character.

beauty is not everything, although we can joke that girls only care about the physical or material aspect, the truth is that a real woman looks at more important things, besides intelligence and personality, there are other attitudes that make irresistible to men who are 'unattractive'.

for example develop your sense of humor.