BDSM Couples, what is your process for negotiating scene content with your partner?

Sometimes sex is spontaneous, sometimes its a release that built up over hours of tension. In our more spontaneous moments, my partner and I typically have a small back and forth right before we start about what we're in the mood for. We usually just agree on a theme or mood, "Sweet and gentle", " Rough with praise" etc. How do you decide together in those moments how to proceed? Do you pause for a discussion, or do you just try and go with the flow?