Scrum teams need to prepare backlog items for future sprints. This is called backlog refinement. Items for the next one or two sprints need to be "ready." But getting backlog items ready is not a goal in itself. Only just enough is needed to be able to get backlog items to "Done" smoothly during a sprint. A balance must be realized in terms of how much, how far ahead, and how collaboratively backlog refinement is done. You must continually inspect and adapt this balance.