If you oppose the idea of making your software easy to install, please watch this video from the FOSDEM '18 conference, How To Make Package Managers Cry.
Look for dependencies ONLY where told to. Do not hard-code search paths for libraries, etc.
Use standard compiler variables such as provided as environment variables or make variables.
CC, CFLAGS, CXX, CXXFLAGS, FC, FFLAGS, CPP (this is the C preprocessor, not C++ compiler!), CPPFLAGS