Transitions sometimes take me forever to mull just the right starting place. "Forever" might equal three days or more. For a productive writer who likes writing, that mulling stage seems like a dead end. I think some people might consider that to be Writers Block, but I don't think that way.
I think positive, that this mulling stage is only a nesting time for when just the right idea, or the right scene makes for a good transition in the story line. Frequently, transitions are used to jump the scene ahead to save space. Other transitions can be done with change of POV or with mood.
The next thing is Who Owns the Scene, in whose head are we? That is most important in every scene. Who owns the scene, or is it narration?
To balance this, consider what the scene is and who it most affects? That is who owns the scene. Sometimes just stopping and weighing who owns the scene makes for an easy transition, that is a change of POV.
Take the scene, consider who is most affected by it, which character feels most deeply about it, add a powerful first jump line and you're generally off and running with a transition.