Eliezer Yudkowsky once wrote that
[...] when you look at what Sherlock Holmes does - you can't go out and do it at home. Sherlock Holmes is not really operating by any sort of reproducible method. He is operating by magically finding the right clues and carrying out magically correct complicated chains of deduction. Maybe it's just me, but it seems to me that reading Sherlock Holmes does not inspire you to go and do likewise. Holmes is a mutant superhero. And even if you did try to imitate him, it would never work in real life.
A few days ago I was at an acquaintance's house after watching the Sherlock miniseries on Netflix. My mind whirling with the abilities displayed by the titular character and I wandered around the house while others were making small talk. I stopped by a large oil painting on one wall that was decent but had obvious problems with perspective. Additionally, it was missing a signature in the lower-right corner.
Sub-par paintings don't generally get put on the market.
If the hostess thought it was worth putting on the wall, it was most likely because she had an emotional attachment to the piece.
Painters place their signatures in the corner of the painting to identify themselves as the creator. If the painter didn't bother leaving their mark, it was because they were confident that they didn't need to.
The conclusion I drew from this was that the painter was either the hostess herself or somebody very close to her. As it turns out, it was the hostess.
Now, this anecdote hardly proves anything. Still, I think it's a fun little thing and the ability to show off like that, even a small percentage of the time, is too good to pass up. So I present my analysis of How to Become a Regular Sherlock Holmes.
1) Pay attention to details. Look around you at your environment. A scratch on a wall, a limp in somebody's walk, a smudge on somebody's cheek. At this point it's probably hard to tell what details are important, so pay attention to everything.
2) Answer these two questions:
"What am I looking at?" and
"What could it mean (if anything)?"
3) Check your guesses.
This is an important step. It's easy to make any sort of judgments about the details and what they mean, but if you accept your own conclusions without checking the facts, you're likely to create false assumptions and associations that you take as fact. That's the opposite of what we're trying to do here.
Fortunately, checking your guesses is very easy to do in most situations with another person. Just state what you've noticed and ask for information on the context. For example, "I've noticed a large scratch on your end-table. Do you know how it happened?"
A follow-up question might be "why haven't you changed it out for another one?", but only if you think getting the information is more important than the possibility of being seen as rude and the potential consequences thereof.
Pay attention to details
"What am I looking at?"
"What could it mean?"
Check your guesses
Oh, and the painting I mentioned at the beginning? I actually didn't figure it out until she told me. I just about kicked myself when I realized I could have figured it out myself and pulled off a really cool Sherlock Summation if I hadn't asked first. C'est la vie.