I like to work in Sprints or on increments of work with feedback loops on all deliverables. I believe a work item can only be declared 'done' once it has been reviewed against its acceptance criteria by someone other than the task assignee, be it a Quality Assurance specialist or a Customer receiving the deliverable.
I involve customers to review mock ups and previews as well as when work is ready to be deployed to a live site. Work is kept to small increments so that things can move fast and risk is mitigated.
Data provides objective insights into how a site is being used. I make use of Google Analytics, Tag Manager and Google Optimize to track site goals and conversions. Google Optimize is an easy way to add A/B and Split testing to help tune site content and design. I like to have experiments running on every major site goal at all times.
A working website that is ready to go live
A list of adjustments and additions to make to the site and the build process to improve the site and speed up developments