Sometimes you don't have any time to prepare for a workshop, or a meeting might unexpectedly turn into a workshop. In such cases, the following method can be used:
Expectations: Ask each participant to write down their expectations on a sticky note.
Turn expectations into goals: Group these expectations to reveal possible goals for the workshop.
Timing: Define a time limit for each group of expectations. Some expectations may not be covered during the workshop and can be put into a category called "parking lot." Add a 15-minute buffer to allow for unexpected conversations, even for short workshops.
Bonus: If needed, define the collaboration settings (i.e. working individually, in subgroups, or altogether).
For shorter meetings or workshops, do a round of expectation setting and put them in the right order, and then start with the first one. Try to stick to the end time in an improvised fashion.
Obviously, having more time to prepare workshops is always nice, but sometimes you just have to go with the flow.
Doing these small expectation-setting exercises at the start of the session doesn't take much time and can still provide valuable results.