Positivity is a good default, but sometimes it's more effective to organise by elimination.
If you explicitly don't want to discuss something - for example, I don't want to get into the build details of an upcoming project until I understand the business case and the why - it can be useful to set a negative agenda. This takes the form of "we'll discuss X, but not Y".
On a current software project with an utterly immovable deadline and wide-ranging scope, I've started maintaining a separate "WON'T DO" backlog - a reminder not to think about, talk about, or plan for any of the items in it. This helps to surface to stakeholders that there is zero chance that we're shipping any of this - which can aid in having hard conversations early rather than on deadline-day - and creates vital headspace for developers.