The term the Golden Rule refers to a commonly believed moral principle that stems from the following biblical verse: "Do unto others as you would have them do unto you" (Matt. 7:12). The principle can be interpreted to mean that we should treat others the way we want to be treated. There are certainly a couple of different moments in Harper Lee's To Kill a Mockingbird when Dill acts based upon the Golden Rule.
One moment when Dill acts in accordance with the Golden Rule is found in Chapter 6. In this chapter, Dill and Jem decide to try and sneak on to the Radleys' property to try and get a glimpse of Arthur (Boo) Radley through a window. When shots ring out, the children flee for their lives. During the escape process, Jem gets his pants caught on a barbed-wire fence and must abandon them to escape. When the children reach the Finches' front yard, they see that all their neighbors have gathered around Nathan Radley, Arthur's brother, in front of the Radley gate to discuss what had happened. Jem argues that it will look suspicious if the children don't join their neighbors to see what all of the commotion was, so Jem arrives sans pants. When Miss Stephanie notices his lack of pants, the kids know they must do some fast thinking to prevent Atticus from finding out what they had been up to. Dill, always the quickest thinker, is the first one to come up with an excuse to offer, as we see when he explains the following to Atticus:
Ah--I won 'em from him. ... We were playin' strip poker up yonder by the fishpool. (Ch. 6)
In taking the initiative to save Jem's neck, Dill is demonstrating that he is treating Jem in the same way Dill wishes to be treated, and Dill gets his wish. When it looks like Dill will be in trouble with his Aunt Rachel for playing strip poker, Atticus is able to talk her out of her tirade, saying it's a phase all children go through and not a big deal.
The second moment Dill demonstrates he is a firm believer in the Golden Rule is when he breaks out into sobs during Tom Robinson's trial and must be escorted out of the courtroom by Scout. Dill explains his reasons for crying to Scout in the following:
It was just him I couldn't stand. ... That old Mr. Gilmer doin' him thataway, talking so hateful to him-- (Ch. 19)
In other words, Dill didn't fail to notice just how antagonistically Mr. Gilmer, the prosecuting attorney, was speaking to Robinson during Mr. Gilmer's cross-examination of Robinson, and it made Dill feel sick inside. Dill's feelings and reaction clearly stem from the fact that he firmly believes in adhering to the Golden Rule, as he demonstrates when he further says the following to Scout:
It ain't right, somehow it ain't right to do 'em that way. Hasn't anybody got any business talkin' like that--it just makes me sick. (Ch. 19)
Since Dill demonstrates he firmly believes all people deserve the same amount of respect, he further demonstrates that he believes in adhering to the Golden Rule.