3 ideas
Gather and register specific observable facts before constructing any explanation, because theorizing too early causes you to twist facts to fit the theory rather than the theory to fit the facts. The discipline is to suspend the urge to conclude until the evidence accumulates, treating small unnoticed details — a worn sleeve, a splash of mud — as the actual data from which inference proceeds.
When you have systematically ruled out every impossible explanation, whatever remains — however improbable it seems — must be the truth. This converts a search for the right answer into a process of disciplined elimination, where improbability alone is not grounds for dismissal once all alternatives are excluded.
Ordinary perception is passive and registers almost nothing of value, while genuine observation is an active, trained skill of noticing what is significant and what is absent. The difference is illustrated by knowing the number of steps on a staircase you climb daily — seeing them every day yet never observing them, because you never deliberately directed attention.