Just sit down and start chewing on it.
Don’t think: I should finish this within X days/weeks/years.
Read it sentence by sentence, pausing whenever you encounter anything you do not understand, and then apply all means at your disposal to understand it (including asking others, letting your subconscious do its work, etc.). Do not set any time limits for this, but don’t give up on it either, but whenever you are stuck and wrestling with something say to yourself: this is precisely why I have embarked on this enterprise. It is only when we are stuck that we have a real opportunity to learn something.
I am sorry to say that I never took this advice myself, while I was still in academia. I have mainly applied it when reading texts in ancient Greek, forcing myself to understand every line, and every odd grammatical detail that didn’t quite make sense to me. This was purely a hobby for me. And this is key for me: there shouldn’t be any additional pressure other than the pure drive to know and understand. When you are in academia, this is very hard to achieve, maybe even impossible.