This is definitely an underrated (but important) skill to develop when working on cases. Usually, the people I've worked with have adopted the same format you currently have with some minor tweaks:
- Position of paper is horizontal (adds more space for the issue tree going from left to right)
- Set space for a column to the left where you can jot down notes from the initial prompt / question asked
- Draw a line on the top of the page for you to write the objective / key question of the case. This is especially important because you will refer to this throughout the case.
- The remaining portion of this first page will be dedicated to the issue tree (with your hypothesis included above the issue tree)
- Lastly, and this is based on preference, write the page number on each paper you use (think of your notes as "draft slides" that you'll place in front of your current "slide" to use as reference)
From then on, although you won't have new objectives, you will definitely be given new information. So, it's usually good practice to structure the remaining pages with a narrow column to the left and space for calculations, new issue trees, etc. What's important, nonetheless, is making sure that you highlight key pieces of information that add substance to your hypothesis. More often than not, we tend to overlook or forget certain points that are given to us. So, by highlighting them or circling them, it becomes easier to connect the dots and, ultimately, develop / finish your case.
When it comes to calculations, definitely keep a separate page but you should practice having an organized sheet that you can cross-reference in case you need to go back through your assumptions and / or calculations.
Hopefully this helps! Keep in mind that everyone has a different structure and it usually takes multiple sessions to find a structure that works best for you. Feel free to shoot me an email if you have any additional questions or would like to practice a case.