Here are a few ideas that I am going to just throw out there. Some may work and some may not.

Make a shot of the Supremacy in TFA.

Have Starkiller base blow up the resistance base on Hosnian.

Have the rag tag fleet be the remnants of those that escaped.

Not so radical, remove all the brain dead humor.

Take out the idea of the resistance in TFA, I never liked that they were resisting the first order but the republic was not. That seems weird.

Make time pass between TFA and TLJ, like months, even a year.

Like I mentioned above, have starkiller base sequence occur at the beginning of TLJ.

Have Luke begin training Rey in TFA and finish (or cut short) in TLJ.

Have the mind link between Rey and Kylo begin in TFA after they meet and she reverses his mind reading onto him.

Have Luke do something to actually warrant his death, like destroy the Supremacy.

Make Poe less of a Mary Sue, he has plot armor and knows it, the audience knows it, he can say anything and do anything because he winks at the audience. Reduce this greatly. Don’t make him such a good pilot that he makes Darth Vader’s piloting look worthless. He makes the bad ass and very serious fighter pilots from the OT look worthless and chumpy. Cut up his ridiculous attack run on Maz’s planet and dreadnought attack run. Give it some drama. It is one thing to be a good pilot and another to be far beyond the skills of anyone ever. He is not a super hero.