They all started with the script, crafted by "Three Kings" and "Red Tails" scribe John Ridley. There's also the book on which the screenplay is based, Solomon Northup's 1853 account of the years of suffering he witnessed and endured on the plantations of Louisiana.
Beyond that, each actor had his own methods of research and preparation. Michael Fassbender, who played slave owner Edwin Epps, spent five weeks in New Orleans "working on trying to find his voice, how he moves, the usual criteria that goes into putting a character together, but with probably maybe that much more feeling of responsibility. Because it was a true story and an amazing story, and we had to do justice to Solomon and all of the slaves [who were] a part of that history."
Chiwetel Ejiofor portrayed Northup in the film, and his research was more global in scope. He was shooting a film in Nigeria before heading to the Louisiana set of "12 Years a Slave." While there he visited a slave museum in Calabar, where thousands of Igbo had been taken as slaves, many of them ending up in Louisiana. "When I got to Louisiana it was about getting onto different plantations and getting a real sense of, not just this story, but of all the different stories that were going on."
There were also practical considerations for each actor. Sarah Paulson, who played Mistress Epps, spent much of her time on set under many layers of mid-19th-century fashion. "I read a lot about the way people walked and moved in clothing, but that also became very clear to me once I put the corset on," Paulson recalled. "It was very clear how one would walk, which is like you can't. So you might as well just accept that reality that you can't sit and you can't eat and you can't drink and all that other stuff."
Since Solomon Northup was an accomplished musician, Ejiofor had to learn how to play the fiddle — or at least how to appear to be playing it. His own guitar skills helped, but they only took him so far. "It turns out that the violin is a very difficult instrument to fake," Ejiofor said. "It's a pretty difficult instrument to play, obviously, but also it's sort of impossible — you can see it if somebody's not playing it, you know what I mean? You can see it a mile away."
But Ejiofor's fiddling ended as soon as the shoot wrapped. "There was a point in my life when I'd pick up something to work on for a part and then I would try and carry it into my life," he said. "And I realized that actually that's not the skill that you develop as an actor. The skill is that you learn something over a very short period of time, but you learn to do it with some proficiency, but then it's important that you just drop it so that you can pick up the next thing when that comes along. I can do a little violin, a little Brazilian ju-jitsu, a little saxophone — I'm very entertaining on a Sunday afternoon."