Most likely, by reading the script over and over
In several interviews, Sir Anthony states that his preperation method hasn't changed in over 30 years.
From Anthony Hopkins has a method to his technique:
Hopkins, who has made seven movies in the last two years (including the upcoming “Slipstream,” which he wrote and directed), acknowledged that atmosphere on the set and time spent in rehearsal play an important role in getting him into character.
“Making a movie is a fascinating process, and I have always loved the process,” he said. “The way it works is that I show up at the location in the morning and grab a cup of coffee. I go to hair and makeup, and put on the character’s clothes. I talk to the director and the other actors. The camera crew comes in and marks the set. We go through some rehearsals.
“By the time I get through with all that preparation on the set, and the reading of the script over and over again, I’m into the character. And I have been doing the same preparation for roles my entire career. It works for me. It’s as exciting to me now as it was 30 years ago.”
In an interview with the Hollywood Reporter, he explained how often he'll read a script:
The Hollywood Reporter: I hear you've perfected a process of preparing for a role that involves drawing wagon wheels.
Anthony Hopkins: It's a method I use, nothing mysterious about it. I learn the text cold, read it maybe 100 or 200 times. The wagon wheels are little four-pointed asterisks with circles around them, so four of those represent 20 read-throughs, and they make my script look interesting. It's kind of phobic, I suppose. (Chuckles)
In terms of the props, it's likely the props department showed Sir Anthony how to use the bone saw and stair truck safely.
From, 11 Behind-the-Scenes Secrets of Prop Masters, Joanna Tillman, a prop professional explains that an actor is focused on acting, and may need coaching on using even the simplest of props:
Union rules specify that a prop is any object touched by an actor, which means prop people have to think about the human side of the equation as well as how things look. They have to watch out for the safety and comfort of the actor at all times, whether that means testing cocaine or teaching actors how to use an AED. “A lot of the time you’re handing an actor something they could hurt themselves with, so you have to communicate,” Tillman says. This goes for common household items, like spray bottles of Lysol, as well as more dangerous props.
“The objects that we use in our everyday life, as soon as you put it on camera and give it to an actor it becomes the most foreign thing in the whole world. Normally people think ‘I won’t spray myself in the face,’ but the actor is doing a lot of work on their character.”