This is how I prep for a placement. Firstly, find a good and reliable textbook. I'm a huge fan of the Oxford Handbooks - not the cheapest but they contain pretty much the foundation of what you need to know for each specialty. I then turn to the relevant section and read the whole chapter. After this, I make notes on each condition mentioned in the chapter. These notes range from brief to more detailed depending on the learning objectives my university have given us (unfortunately, I'm not able to share these but your university should give you a list anyway).
As you can see below, I highlight things using Zebra Mildliners and the notes are kept super brief. These notes accompany me on placement so that I can refer to them easily if needed. For me, these are just brief notes as they are messier than my revision ones.