Go back before they started writing the film and make sure that Stewart and Spiner have absolutely no input.
That's pretty much the solution to the problems of all the TNG films.
What input did those two have in the writing of GEN or FC?
I don't know about Generations
. However, Patrick Stewart's input heavily influenced the story direction for First Contact
. The early drafts were very different. In the early drafts, Picard was on the surface throughout the film and actually ended up having to assume Cochrane's place and make the warp flight to set history right. Riker was on board the ship and led the fight against the Borg.
You may disagree, but I like it better that way. Even though Picard has a history with the Borg, he is the thinker. He is the historian. He, to me, is a more logical fit to help restore history. Meanwhile, throughout the series, Riker is the action guy. Leading the fight against the Borg seems a natural fit for him, particularly since he led the fight against the Borg in "Best of Both Worlds".
The biggest problem of the TNG movies is that they became the Picard & Data show, and Stewart and Spiner had a lot to do with that.