There should have been certain things we know from the later episodes mixed with surprises but filtered in such a way that if seen in order the plot revelations in later episodes could be maintained for future generations.
Obi-Wan should have been trained by Yoda directly he should have discovered Anakin (a young adult and already a great pilot) and amazed at how strong in the Force he was took it upon himself (not at the bidding of a never again referred to other Master) to train him as a Jedi.
Yoda should never use a lightsaber and be cautious about the use of Military force.
Anakin should have had a strong relationship with his full brother Owen and his sister in law Beru and followed Obi-Wan out of principle with terrible results.
Anakin's wife should have survived for some years after the 'death' of Anakin.
Vader should have been disguised in some way when he fought Obi-wan and maybe Anakin should have stolen the identity from another pupil of Obi-Wan's so that first time viewers could believe that both characters could be separate and still be shocked by the revelation in ESB.
The cyborg Vader should have been introduced much earlier too (no need for General Grievous).
Outside that Lucas could have told pretty much the same story but concentrated on making the characters believable and the fantasy grounded in the same sort of logic that ANH and ESB were.
P.S.Did Anakin's wife have to be a Queen/Senator BTW? Leia is Princess of Alderaan because of her adopted father so her real mother could have been anyone. He could have married her before becoming a Jedi too it's easier to follow characters already in love than develop a romance from day one (especially if you are Lucas).
Most importantly Lucas should not have written it all and only directed maybe the first one if that.
ANH and ESB worked because they were team efforts pushed by his energy the rot set in with ROTJ and Lucas should have realised this and played to the strengths of what worked before.