Connect several clues to an interpretation, then check whether another explanation remains possible. An inference can be well supported without giving access to a character's unspoken thoughts.
Worked example
A speaker rehearsing twice and checking notes may be preparing carefully. That does not prove the speaker has never presented before.
Original fiction: The Paused Reply
Omar read the invitation, typed a reply, and then deleted it. He checked the project calendar before writing again. This time he sent a short acceptance and added the event to his schedule. The passage does not include the deleted words. It also does not say whether his first draft was too long, had a typo or offered a different answer.