Make Boba Fett just Jango’s son, not a clone.
Have Dooku just defeat Anakin and Obi-Wan and then leave. No Yoda fighting.
Have Dooku play a larger roll in Ep. III, keep him the instigator of the Clone Wars, there’s no real reason for Grievous, he’s really just an extra character.
Cut the whole opening of Ep. III, it’s just tonally inconsistent with the rest of the trilogy and doesn’t really serve a purpose if Grievous is cut out.
Speaking of extraneous characters, make Obi-Wan closer to Qui-Gon’s age and more active in the plot, especially Ep. I. Qui-Gon ultimately doesn’t have much purpose to the saga and it would have been far more effective if Obi-Wan trained Anakin by choice rather than obligation to his master, plus his age in Ep. IV would then make more sense.
Make the Jedi not-cradle robbers.
Make the Force Ghost thing not be something to be taught, but return it to a natural state that Jedi pass to when they become Force ghosts.