Progressions in C — 5-String Banjo

C major harmonises to C – Dm – Em – F – G – Am – B°; C minor to Cm – D° – D# – Fm – Gm – G# – A#. Each chord links to its 5-String Banjo voicings, so a tune in C becomes a short list of shapes before the first repeat.

Then check the key against the short g: some keys let it ring free through every change, and some make it a note you have to work around. Knowing which is which is most of what "playing in a good key" means here.