The Shizuoka Prefectural Central Library (静岡県立中央図書館)'s ongoing series on decoding historical documents written in cursive is really very decent, especially for something available online for free. It's more like an apprenticeship than a first-principles how-to, working through actual (short) texts character by character, and I particularly appreciate the way the instructor "shows their work," so to speak, saying "this character looks like X, but if we read a few characters more we can see that it's actually Y." (The very second lesson is called "Form hypotheses as you read," and is about this process.)

The peak to strive for, no doubt, is the ability to identify even the most carelessly scrawled characters in isolation, but slogging through actual texts as best you can has always been my preferred way of learning.