Maybe find some nice challenges or a project that you can build at the same time as you modernize your Java skills?
E.g. Cryptopals or Project Euler.
Maybe start just by reading blogs and tutorials, find areas to concentrate on.
After you get started, maybe get on board with some Open Source communities. There are lots of helpful people who will be willing to chat and help you, if you're minimally competent in the project. That human interaction can be a big booster, IMHO.
Head First Java, 3rd Edition (May 2022) - https://www.oreilly.com/library/view/head-first-java/9781492...
This issue is for both C++ and Java. The best books are over a decade old and not quite right.
Definitely this book: https://www.manning.com/books/modern-java-in-action
There is no best way. Just start and power thru it until it makes sense and you can complete a good size project. I'd suggest an android project but that's me. Pick something useful to you.
Here's a book to get you started:
https://www.amazon.com/Java-Beginners-Guide-Herbert-Schildt-...