The following changes would improve the Sequel Trilogy:

Remove Starkiller Base’s superweapon powers and its destruction. Make it just a military base. The movie should stick to the search for Luke plot.
When Kylo asks Palpatine how he survived, have Palpatine say, “Did Luke really think I was foolish enough to send my true body to the second Death Star?”
Have Palpatine say “bring the girl here” instead of “kill the girl” and have him drain Rey and Kylo as soon as they arrive rather than trying to essence transfer into Rey.
More world-building. Do the people of the galaxy and/or the characters know that Count Dooku and the Trade Federation were working for Palpatine?