Richard Feynman mentioned a paper that was very hard for him to read. I can't remember if it was in his bio or letters volume (I think the former, have both). He told his sister that he just couldn't handle it...was too hard. And she counseled him to just sit down and push through it. And he did...and once he'd done it, said it wasn't that bad. I know that it sounds minor, but I can just imagine how he felt.
One minor idea to add (not listed yet). I have found in the physical sciences, that pulling every reference, and printing it and skimming/reading them, can be very helpful. I wouldn't say that I get everything when I do that. After all the paper was already tough for me. And the volume of content has increased. However, I still find things that way...unexpected easy explanation, new gems, etc. Sometimes I even pull all the refs to the refs (one layer down of turtles). You really do start to get a gestalt that way. For example, with the one layer down of turtles, you'll start to see repeated key refs in the field. Also...practically, I find that killing trees and filing them in subject folders is a key aspect of this. You'll never get it to work, by online skimming. But if you kill the trees, it somehow works in a way that skimming the physical shelves of a library works. (Also, having them in a file cabinet, means you can go back to them in other contexts, in a way that you would never do if electronic...and more easily hidden/forgotten.)
