Make simplified pencil diagrams for each system, and learn what they have in them and how things connect. It takes some effort, but draw and redraw the system in question until you can do it from memory without looking at the key. Do it not so much from rote memory as a sense of how this component supports that component, and that component affects the other. A purpose- driven view is what you are after and will remain with you the longest. Once you master one system go onto the next one until you master them all. It helps to make sure you have a good simplified drawing to start with, and if the school does not provide one, then run your pencil item by an expert and make sure you have the correct scheme. Most official manuals give diagrams that are overdone for pilots, and can be simplified quite a bit without losing the essential meaning. You will be amazed how fast you become and expert on the various systems this way, maybe an hour or two each system should be enough for basic turbine aircraft.