I've been at this a while, and have been at 0 nic for a while before. Currently I'm up to around 6-10. Hey, at least I haven't gone back to analogs!
What's worked for me is to step down gradually. When I was at 24mg I stepped down to 12 by using the 12 over a full weekend just to see how it would go. Then over the course of the next week I used 12 most of the time, but kept a tank filled with 24 just in case I was jonesing for it, which I did go to especially just after lunch (a big "trigger time" for smoking for me). After that although I kept some 24mg around for a while, I found that I didn't need it.
Grace's idea sounds like it should work too. The basic idea is the same. I've found that once you have stepped down for a while and realize that you aren't freaking out then you're good to go.
0 nic is a different story. Although I've been able to be on 0 nic for quite a while (a few weeks at a time), I've somehow always relapsed back to some kind of low nic. One of my problems has been that some juices don't taste nearly as good without it (not sure why that is). At least I'm stable at 6-10mg. And to be honest, I'm fine with that. I mostly use 6mg, but when I feel the need, I'll bump it up a little. 12mg is now too strong for me to vape (I get the jitters), even when I'm stressed out.