If you're new at facilitating meetings, preparation, especially in the beginning, is extensive and burdensome. It will be, simply, trial and error until you figure out what works best for you and your team, in your unique environment. You should be your own worst critic; make observations and notes about what is and isn't working during your meetings, and ask the team members for their feedback as well. Meeting results are directly proportional to your preparation and your overall facilitation experience.
The product backlog powers sprint planning. Just as engines run more efficiently with high-octane fuel, teams can plan more efficiently with well-prepared product backlog items.
I've found Bill Wake's INVEST acronym to be the best readiness litmus test for PBIs coming into sprint planning. INVEST stands for Independent, Negotiable, Valuable, Estimatable, Small, and Testable:
