"The trick is you have to document everything you type step by step. The problem programmers have is they know how to install this stuff like it's second nature, so they skip details and important steps that non-programmers just don't know. Once you have your instructions, erase the machine (or VM) and go through the steps again, manually. You'll run into stuff you missed and will need to fill those missing steps in."
This applies to a lot more than writing a book and is great advice to anyone who is writing documentation for their code/project. I find this technique particularly helpful when writing a "How to get our development env up and running in 3 hours or less" document.
Most of the time I just write it down in a Google doc and share with my team. But lately I've been documenting all steps with Fabric, which has the dual benefit of being very readable ("self-documenting") code as well as a one-command setup script 'fab -h <target>'. And the way I create my Fabric scripts is basically what Zed describes above.