The Surprising Power of Documentation
I can't stress this enough. Know your audience and tailor your documentation to them.You should write three types of documentation.  One for users, one for admins and one about architecture.User docs are simple. How do I use it. What are the API calls, etc.  Admin docs are about how to install/break-fix/troubleshoot issues that are beyond user interaction.  Architecture is how the system is constructed, why certain tech was chosen, etc.There's nothing that makes documentation more useless than when you're trying to do something like install the software but you have to dig thru piles of docs about why Postgres was chosen over MySQL. If your users or admins cant find the info they need quickly, they'll soon discard the documentation and user/system ops will go back to word of mouth knowledgeable.I really think good companies focus on this and those who are successful really shine.