Comment by michjedi

Books.

I read about 30-100 work-related books a year and have seen salary double every few years.

I try to alternate books between different areas, more or less from these sections:

Technical(on currently used technology)

Technical(unused tech vaguely related and may be useful)

Management

Domain(scientific textbooks, best to search from related university course reading lists)

Biographies/accounts/events of typical and super users