I'd rewrite the ending of The Force Awakens so that they don't destroy Starkiller Base at the end. Instead they'd just damage it heavily or somehow disable it. A victory for the rebels, but now we have a story for the next movies.

Then the second movie would then have to be rewritten to be about the First Order trying to repair Starkiller Base, perhaps they need some rare resource or something, and the rebels are trying to stop them. We get a bunch of space battles and AT-AT walkers and stuff.

The third movie would then also have to be rewritten. The First Order has got the thing working again, so the rebellion would get to destroy it for good this time. More space battles, lightsaber fights, and big explosions.

Really, the problem the sequel trilogy had is that they didn't know what to do with it. The Force Awakens ended up as a soft reboot of A New Hope, which is why we got a third Deathstar. But then they blow it up at the end of the first movie, which puts them in a bind as now they really don't know what to do with the next two movies. What now, a fourth Deathstar? At least this would give some sort of overarching story for the trilogy, rather than the making-it-up-as-we-go mess that we ended up with.