The problem with tuning a 12-string is that you can lose track of where you started, and end up tuning a string that is on pitch to match one that is out of pitch, rather than the other way around. This can increase tuning time exponentially.

The easy way to avoid this is to simply tune it like a conventional six string first, then go back and match up the octave/unison strings. (which would generally mean tuning the 2nd string in each course first.

Not only is the 12-string a significantly different instrument from the 6-string, 12-strings from different makers often seem like different instruments entirely, requiring significantly different playing techniques, and offering different musical possibilities.

I had an old Harmony Sovereign that played like a regular six, and have played a good Mexican 12 that had to be fingered more like an acoustic bass. I once ran across a luthier-made half-size instrument that was   more like a melody instrument--