Get your farm / tenant working first.
Do not let end users into your development environment. Do not let test become production.
Don’t spend all your money on branding. Get the value of SharePoint Content Management and Collaboration first.
Start with a Governance Plan before anything else. Define responsibilities and project scope.
Architect SharePoint Site Collections based on content and permissions.
Build out Metadata and content types before moving content. Users will not go back and fix this if it is not done up front.
SharePoint is a Content Management System (CMS). It is not a network share or a file dump.
Maintain the One Truth.
Train the users that will be the administrators: the ones that will be asked to manage permissions. Management may want to be included but they will not be the ones that will respond to user requests. Create separate training for management and end users.
Create a Community of Practice.