In preparation for the role, David Suchet read every single book and short story Poirot appears in: "I had my file on one side of me and a pile of stories on the other side and day after day, week after week, I ploughed through most of Agatha Christie's novels about Hercule Poirot and wrote down characteristics until I had a file full of documentation of the character. And then it was my business not only to know what he was like, but to gradually become him."
During the filming of the first series, David Suchet almost left the production during an argument with a director, insisting that Poirot's mannerisms (specifically, putting a handkerchief down before sitting on a park bench) be featured.
Days before filming David Suchet would often dress up and act as Hercule Poirot. He would immerse himself in the role by acting like the detective even with his own family at home. This made his transition to the role easier when filming started.
While at least some of the stories take place in 1935 (in Agatha Christie's Poirot: Murder in the Mews (1989), the date of Guy Fawkes Day is given as November 5, 1935), Florin Court in Charterhouse Square, the building that serves as the location of Poirot's flat, wasn't built until 1936.