There are many possible tunings for an 8-string guitar. My favorite is G-6th with a low E. I feel at home with this one because it includes the basic strings I already know from playing a Dobro. Starting with the lowest string, the tuning is…..

E G B D E G B D

For my double-necked guitar, I have been tuning the second neck to a Texas/Oklahoma style of E-13th, like this……sometimes I will retune the D or F# in the middle to plain ol’ E.

E G# D F# G# B C# E

I have also been fooling around with a variant of C6 but it’s not ready for primetime.

F A C E G A C E