My method is to alter the resolution at which I'm perceiving the matter, by zooming out and taking a low-resolution mental representation of the entirety.
Squinting at the matter (so to speak) blurs the resolution, so regions of complexities coalesce into a handful of bundles. And although blurry, the picture is simplified and becomes more mentally manageable.
Then with each over-simplified bundle of complexity, we can start to unpack and re-evaluate the contents inside. Becoming more granular, correcting biases and adopting a nuanced understanding of the matter underneath.
Working in iterative cycles of; drilling into each bundle and zooming back out, like slicing through a cake, we get a tour of the whole and gain a deeper insight.
Along the way, reoccurring patterns form and when durable enough, can speed up our analysis of the remainder of the content. These emerging patterns can appear as classifications, metaphors, relationships, analogies or anecdotal examples to aid in succinctly communicating the gist of complexities to others and ourselves.
In the end, this technique culminates in a comfortable understanding of the complex whole. An expert grasp is not necessary, we only need enough comprehension to define our goals and propose the next logical steps forward.