Hi paradiseseeker,
My wife and I talked about leaving the faith a few times before we actually did. Almost immediately after I was appointed an elder I became disturbed by how this part of the faith functioned. I already had some serious doubts about the existence of God, Noah's flood and how we treated the theory of evolution. But we were both greatly frightened by the prospect of leaving. So we hung on for a few more years.
When we left it was dramatic. Out in service Saturday morning and left that afternoon. But a circumstance surrounding my daughter was a catalyst. Two years previously I resigned as an elder and was now more comfortable with the idea my doubts about the existence of God was not going to go away.
Once a person has decided I don't think there is much reason to delay. In most cases I recommend against writing a letter of disassociation. Unless the person is still in agreement with the rules of the faith there is no real obligation to follow their formulas.
Leaving was a bit disorienting. I found keeping all the other parts of my life in a routine helped. Work was still there. My family was still there (in my case my wife and daughters left with me). I took up running, which helped. Eventually we found an Ex-JW meetup group and that was great (mostly). I say "mostly" because one of the two groups near us was oriented towards getting JWs to become nominal Christians -- which I wasn't interested in.
The cold realization that so many friendships in the faith are conditional came as a shock. Literally nothing about my person, how kind I had been or continued to be made a difference. The depth of the influence the faith has over those who believe was more than I ever thought.
Adjusting to the world outside also took time. As awful as the JW life was, there is something to being part of a small group who self-style themselves as "us against the world." There is an odd reality to the "brotherhood" that I found doesn't exist in the larger wider world. The good news I found is with some work relationships you do gain are built on a much better foundation. The ability to really listen without judgment is great. I eventually joined another religion (Unitarian Universalists) who accept atheists.
It wasn't easy to leave, but after being out for all these years, we are so happy to have it in our past. My wife and girls love Christmas!
Take care, -Randy