Long planning meetings feel productive, but most of the time is spent discussing tasks nobody will start this week. A good sprint plan fits on one screen.
Start with one sentence that describes what will be true at the end of the sprint. Then pull only the tasks that move that sentence forward, and estimate them with the people who will do them.
One goal, one screen
A plan that nobody can read in a minute is not a plan, it is a wish list.
Leave twenty percent of the time free for the unexpected. If everything goes well, you will finish early; if not, you will still deliver what you promised.