I write mine with a simple mindset: "imagine we go outside with a net, catch a random person off the street, sit them at the PC and tell them to do X. Will they manage, following this documentation?"
I also number every step (even if they're stupidly simple and could technically be jumbled into a single sentence), so that when a user calls me asking for help with something documented, all I need to do is ask them "at which step of the instructions are you encountering the problem", and then they hang up because they never read the instructions in the first place. Saves a lot of hassle!