Decision sketching is the practice of quickly iterating through a structured decision making process to understand what makes the problem hard and where more time and effort are warranted (Gregory et al. 2013). It can be done individually or in a small group to start thinking through a problem before bringing in other perspectives, if warranted. Be prepared to iterate on this and be open to changes as you develop new insights along the way.
Here is a decision sketch template that we use internally: