Progressions in D — 5-String Banjo

D major harmonises to D – Em – F#m – G – A – Bm – C#°; D minor to Dm – E° – F – Gm – Am – A# – C. Each chord links to its 5-String Banjo voicings, so a tune in D 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.