Use some logic, you have access to the formula sheet that will be provided, so you know what doesn't need to be put on it.
Your sheet should be personal. Add examples that you need to remind youself of. Remember they cycle questions, they'll adjust the values, but the questions themselves are often repeated. Other than that, for qualatative answers, list the key points.
Hope that helps.
The physics cheat sheet can be a maximum size of A3 and double sided. I would organise the cheat sheet by topic. While you're studying during the year make concise summary sheets on each topic as you finish them (even better, make cheat sheets for SACs if your teacher allows them). Create them while the topic is most fresh in your memory, making it easier on your exam revision when the time comes. I would then combine these summary sheets at the end of the year which I would recommend contain derived formulas to make it quicker to answer questions in the exam, dot pointed explanations on the theory and examples if you need. As dvermont said, the physics exam (by the most part) repeats itself a lot, so my number one piece of advice would be to do questions, as after all, that is what you will be doing in the exam. At the end of the day, the cheat sheet is just a safety net during the exam, a glance over to it can calm your nerves and put you back on track. Doing exam questions however is the best way to prepare.
Here's one that itute created which you can use for inspiration: http://www.itute.com/wp-content/uploads/2018-physics-summary-sheets-2017-2021.pdf