As I start to formulate an idea of the Session design, I find this worksheet useful. It allows me to arrange all the vital information (condensed into very brief bullet points) in one organised grid.
When I have more than one Session design in my head, I can jot them down on different sheets and evaluate them together. Once I have arrived at a design I like, I make a clean copy (my worksheets always become messy with corrections, changes and arrows indicating correlations or where to move something). The clean copy is then a useful tool for sharing the design with others and subsequently making any changes.