Personally, using a good debugger and knowing how to use have been more useful to me that anything else. I mainly code in C and C++, and Visual Studio integrate

Personally, using a good debugger and knowing how to use have been more useful to me that anything else. I mainly code in C and C++, and Visual Studio integrated debugger and GDB are my main debuggers (depending what I'm doing). For me is faster to double click the border of a line in VS or writing "break 123" or "break fooFunction" in GDB and stepping and watching how some values changes than adding and removing "printf" lines. Adding some asserts are other thing. They always are good, and often necessary to find some "Heisenbugs". In other languages I probably won't think the same, but I haven't done anything big enough outside C or C++ to give a proper opinion.