I don't use a tuner, never have done... makes your ear 'lazy'!!

Seriously, unless you're gifted with a good ear (as I am), it's the only way. A 12-string that is slightly out of tune is far more obvious than a 6-string.

A useful trick that I've taught people in the past is to fret the first (thinnest) string at the third fret to tune the thinner third string (G), then tune the thinner fourth string at the second fret to the open first (E). Now tune the secone strings at the third fret to the open thinner fourth string (D). Next, tune the second fret thinner fifth string to the open second (B).

If you now get the octaves right on the third, fourth and fifth pairs by tuning the thick string twelfth fret harmonic to the open thin string, all the is left is to tune the thinner 6th to the thicker 4th, second fret (E), then start from the begining again to check that all's well.

Yes, it's tricky at first, but it's very accurate and doesn't rely upon a tuner - except, perhaps, to tune the first open E.

This method does get the instrument 'in tune with itself', and, with practice, can be used to tune to other instruments.

I do so hate people who spend longer tuning than playing...! It looks (IS) so unprofessional!

Okay, perhaps I'm biased because I don't have a problem with it...!!