The OT's Prequel Trilogy Rule Book
1. "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 as a Jedi."
Anakin must already be a great pilot, not pushing buttons going "Oops", "What does this do?", etc. Obi Wan must be amazed by his force powers, not reading the results of any scientific blood tests. He's not going to take over his training as the death wish of anyone else, he's taking it upon himself
2. "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."
Sounds cool this one. Probably get the best part of a film out of showing the fallen Jedi helping the Emperor trying to find and kill the Jedi
3. "That boy is our last hope" "No, there is another"
Obi Wan has no knowledge of anyone else other than Luke who may be able to defeat Vader / The Emperor. Only Yoda knows that there is someone else hidden away. Easy enough this one, just ensure Obi Wan not at the twins birth or even aware that there are twins.
4. "Leia, do you remember your mother? Your real mother." "She was... very beautiful. Kind, but sad. Why are you asking me this?" "She was... very beautiful. Kind, but sad. Why are you asking me this?" "I have no memory of my mother. I never knew her"
Again, pretty simple. Leia lived with her mother until old enough to remember some specifics, Luke clearly didn't.
That's it. Easy. You've got three films to spread this stuff over. Just follow these simple rules and you've got a prequel stew' going...