Start out simply. Examine standard indicators around technical compatibility, broken links, sales opportunities, searches using your internal search tool that return no results, etc… These basic indicators alone will give you interesting information to work with. Before trying to measure more complex things, first get well situated, and then advance progressively.
“You have to nail the basics before you try to get fancy […] Accept that your organization will take time to crawl, walk, then run.”
Michele Kiss, digital analytics author and expert
Read the article “Six rules for nailing digital analytics”