Compression. The more you can simplify what you're trying to learn the better.
Here are some ways to do it:
Breaking concepts into parts and only focusing on understanding one small part at a time. This acts as a 'foothold' for understanding the entire concept, similar to how a foothold in a mountain helps you climb part of the mountain.
Identifying and then ignoring irrelevant parts of the concept (trimming the fat).
Analogizing the concept (or the small parts of it/footholds) to concepts you already know.
Of course there are probably more ways to compress a concept. If someone knows any please do share.
The idea is to work with small concepts in your 'cache'. If a concept is too big you won't efficiently learn it, especially if your short term memory is bad like mine. So, you can break it down into smaller parts and learn each of those, and then combine them at the end. Or you can point to a concept you already know that is in your long-term memory (analogizing).