When the Star Wars prequels were announced, at one point I went over the old trilogy to see exactly what had been established. Since, I've found a lot of quotes and other interesting stuff, regarding the ideas. A quote from The Making of The Phantom Menace, to establish the foundation of the story, in Lucas's own words:
"The story for the three new films was meantto be the backstory of the other three films. That backstory was sketched out in a rudimentary fashion when I wrote the first trilogy, and there were certain things I knew even then. I knew, for example, that there was a character named Anakin Skywalker who grew up on a small planet, had special skills, and was found by the Jedi. I knew where everybody came from, who they were, and how they got to be what they were. A lot of the story points were there. But the actual scenes and many of the characters were not."
This is crazy long, so I'm going to put down a cut.
With that dealt with, let's go to the most basic source of information, the original trilogy's scripts. There are few references to the times before, but they somewhat informative. Obi-Wan Kenobi's recollections from Episode IV (which are later put into question):
"[Owen] didn't hold with your father's ideals. Thought he should have stayed here and not gotten involved."
"[Anakin] was the best starpilot in the galaxy and a cunning warrior. ... And he was a good friend."
"For over a thousand generations the Jedi Knights were the guardians of peace and justice in the Old Republic."
"A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi Knights. He betrayed and murdered your father. Now the Jedi are all but extinct. Vader was seduced by the dark side of the Force."
Then from Leia (in a hologram): "General Kenobi, years ago you served my father in the Clone Wars."
Tarkin referes to the Senate: "The Imperial Senate will no longer be of any concern to us. I have just received word that the Emperor has dissolved the council permanently. The last remnants of the Old Republic have been swept away."
Admiral Motti says of the Force: "Don't try to frighten us with your sorceror's ways, Lord Vader. Your sad devotion to that ancient religion [etc.]..."
And Han refers to "Hokey religions."
Tarkin says to Vader: "The Jedi are extinct; their fire has gone out of the universe. You, my friend, are all that is left of their religion."
Vader says to Obi-Wan: "When I left you, I was but the learner; now I am the master."
Then we move on to The Empire Strikes Back, where Obi-Wan instructs Luke to go to Dagobah, where "you will learn from Yoda, the Jedi Master who instructed me."
Yoda and Obi-Wan give a few interesting tidbits. Yoda: "Much anger in him, like his father."
Then Obi-Wan: "Was I any different when you taught me?"
Yoda soon says: "He is too old to begin the training."
And: "For 800 years have I trained Jedi."
In Return of the Jedi, Obi-Wan speaks of Anakin: "When I first knew him, your father was already a great pilot. But I was amazed how strongly the Force was with him. I took it upon myself to train him a Jedi. I thought that I could instruct him as well as Yoda. I was wrong."
Leia has a vague impression of her mother: "She was very beautiful. Kind but sad."
That's pretty much it. (Remind me if I missed something. I've left out discussion of the Force and Jedi training on purpose.)
There were two deleted scenes that were of interest, too, though of course they can't be taken as canon.
First, in the original movie, Red Leader tells Luke: "I met your father once when I was just a boy. He was a great pilot."
Then in Return of the Jedi, Obi-Wan tells Luke that Owen was his brother!
Finally, the introduction to the novelization of Star Wars reveals quite a bit of information, which corresponds very directly to the prequels:
"Once under the wise rule of the Senate and the protection of the Jedi Knights, the Republic throve and grew. ..."
"Aided and abetted by restless, power-hungry individuals within the government, and the massive organs of commerce, the ambitious Senator Palpatine caused himself to be elected President of the Republic. He promised to reunite the disaffected among the people and to restore the remembered glory of the Republic.
"Once secure in office he declared himself Emperor, shutting himself away from the populace. Soon he was controlled by the very assistants and boot-lickers he had appointed to high office, and the cries of the people for justice did not reach his ears.
"Having exterminated through treachery and deception the Jedi Knights, guardians of justice in the galaxy, the Imperial governers and bureaucrats prepared to institute a reign of terror among the disheartened worlds of the galaxy. Many used the Imperial forces and the name of the increasingly isolated Emperor to further their own personal ambitions."
At some point, possibly years down the road, I will put up things I have found in interviews and other sources, and then we shall analyse them!