How to become a detective (according to sherlock holmes)

Retain only the knowledge necessary.

Study practical geology, anatomy, sensational literature, law, chemistry, and, above all, self-defense.

Know how to vent. Preferably with music, but early on he also used drugs (not advisable).

Study people.

Be completely aware of, and thoroughly study, your surroundings.

Be a master of disguise.

Invest in a really cool hat.