Preparing your documentation and training for a Dynamics 365 upgrade

If you are planning an upgrade of your Dynamics 365 environment, you are probably considering how you can prepare your business for new and revised processes and how best to document the process changes for the end-users. At what stage do you start the preparations? How much collateral is needed to support your end-users in the best possible way? How do you organize your business around an increased update cycle?  And how, in the most cost-effective way, do you create the documentation and training collateral?