The Emperor's chair was mechanized so that it could rotate when the scene called for it. However, the mechanism never worked properly, so Ian McDiarmid had to make it move by shuffling his feet. A piece of tape on the floor told him when to stop so it would not be visible to the camera.
Carrie Fisher really cared about Warwick Davis' well-being during filming, as he had to spend it in a hot Ewok costume. She also provided him with cookies and chocolate milk between takes. Davis later commented "She was everything an eleven-year-old Ewok could possibly wish for."
It took six people to work the full-sized animatronic of Jabba the Hutt. The puppet fit three men inside -two to operate the arms, head and tongue and another to move the tail. A man lying below the puppet pulled strings to move Jabba's mouth and make his sides heave. And two radio operators controlled the slimy goon's eyes, including pupil dilation, direction and wideness of eyelids. A final crew member was responsible for rubbing gel on the puppet to give Jabba his slimy look.
According to Ian McDiarmid, George Lucas originally cast him simply as the physical performance of the Emperor (similar to David Prowse as Darth Vader). This became evident to him when a producer told him that if he was able to get his voice close enough to Clive Revill's (who portrayed the Emperor's voice in Star Wars: Episode V - Das Imperium schlägt zurück (1980)) Lucas would let him use his on-camera vocals in the final cut of the movie. However, McDiarmid felt he could conduct a stronger, more wicked and demonic voice for the Emperor as opposed to Revill's more aristocratic Emperor. Lucas, and even Steven Spielberg, were so impressed with his take that it ended up becoming a signature trait of the character.
During the shot in which Salacious Crumb (the small, annoying, rat-like thing that sits with Jabba in his palace) is chewing off C-3PO's eye, Anthony Daniels had a panic attack while in the C-3PO suit. While filming, he didn't actually say his lines (all of his lines were dubbed in post-production anyway), but repeated "Get me up. Get me up." over and over. This is the take used in the final cut.
Ernie Fosselius: Creator of the Star Wars spoof Hardware Wars (1978), appeared as the voices of the rancor's keepers.
Richard Marquand: One of the two AT-ST drivers who's vehicle gets hijacked by Chewbacca and two Ewoks.