Once you've got the basics down from a tutorial (old C++ or modern C++), move on to internalizing all the lessons here:

https://isocpp.org/faq (what Marshall Cline's excellent C++ FAQ has become)

and here:

https://herbsutter.com/gotw/ (Not as organized, but Herb Sutter wrestles with the essential questions of how to deal with the tricky bits of C++)

If you've got the cash, read Effective Modern C++ by Scott Meyers.

Finally, if you're ready to snark at all you've learned, read the C++ FQA:

http://yosefk.com/c++fqa/