C++ class header files organization

Question

What are the C++ coding and file organization guidelines you suggest for people who have to deal with lots of interdependent classes spread over several source and header fi

Answer 1

One more point in addition to the others here:

Don't include any private definitions in an include file. E.g. any definition that is only used in xxx.cpp should be in xxx.cpp, not xxx.h.

Seems obvious, but I see it frequently.