Thanks for the kind words, Barnabas (always appreciate a Dark Shadows reference, by the way).
I doubt I'd have any advice that isn't commonplace. And the only thing my solve rate indicates is that I've spent a ridiculous amount of time refusing to give up on a puzzle.
I always start by looking at context, especially at the beginning of the quote (and sometimes at the end, or after a punctuation mark)... it's often pretty easy to get a quick toe-hold by seeing something like:
or, "If you want to..."
or, "______ is the ____ of _____..."
If that fails, then I move on to scanning individual words, looking for patterns that jump out at me.
If that fails, it's going to be a long slog... looking at frequency of letters, trying various combinations, etc.
The ones that REALLY burn me are the ones where I know I've broken in and have the basic idea, but also know I might have a thing or two wrong here and there, and there remains a word or two that I just can't figure out. Usually that means I do have something wrong somewhere else, but man that's frustrating.