If you have the tune in your head, it's rather an easy chore to simply know when to change chords----or not to change them. To me it seems fairly easy to do it by ear. But that's always the way I figured out to play any song I ever did.

I did use this fine tune for my version of The Lakes Of Pontchartrain.

(C)It was on the third of January,
I bid (F)Cairo town (C)adieu,
(C)I traveled down the river road
My fortune to renew,(G7)
No (C)money in my pocket,
No (F)credit could I gain,
And my (C)mind it turned with longing toward
The (G7)Lake of Pontchartrain.(C)

That's pretty much it. Just 3 chords unless you want to do it differently. Do it the way it feels correct for what you know musically already. Toss in your own personal cliches -- your own favorite picking or strumming cliches/idiosyncrasies. THEN what you achieve will be in your own style that people will know you by.

I hope this helps!

Art Thieme