The answer is to do it. Do it often, do it a lot, over and over. The linked tweet provided great advice, as do other resources and comments in this thread. But the bottom line is that you learn by doing, and trying hard.
I remember reading the same section of a paper at least 30 times, no exaggeration. I would read it, then go and look up the topic online, then read it again, then go do something else, and then read it again. Over and over for days. i parsed every symbol and word of every line. And then one day I was elucidated. I finally understood it, and it was a feeling of awesome communion with the gods.
I'm not sure if there's a short cut, but I'll be monitoring this thread along with you in the hopes of finding one. Do what the others said and print the paper out, and take a pencil and highlighter to it. Look up terms you don't know online and be diligent in your use of search engines. Just stay at it, and don't give up!
As an afterthought, most modern computer science papers have a graphic or figure on the second or third page that does a good job of explaining the idea visually. Older papers tend not to have this, or it's buried deeper in the paper. Look for this key graphic and use it as a guide or framework to understand the rest of what's being said.