Gee Eddie, that's a good question. My first impulse is to sub-divide the bar - divide by 2 or 4. 6/8 divided by 2 is 3/4 - waltz time. 12/8 divided by 2 is 6/4 and that is nothing like waltz time - divide by 2 again and you get 3/2 which is pretty strange so I would forget it. My point here is to subtly suggest that in my mind, 6/8 and 12/8 are not similar and should not be compared.
So, counting 6/8 as waltz time you get 1, and, uh, 2, and, uh, 1, and, uh, 2, and, uh - two sets of three in each bar. Think Miles Davis's "All Blues".
Griff usually counts 12/8 as "Swing time", in four sets of threes/triplets - 1, and, uh, 2, and, uh, 3, and, uh, 4, and, uh, 1, and, uh, 2, and, uh, 3, and, uh, 4, and, uh. Think Albert King's version of Ray Noble's "The Very Thought of You".
I hope this makes some sense to you, and also hope it's not complete crap
- over to "the more knowledgeable folks" who snarf mentioned.