I know it's a wimpy answer, but it really depends on the site.
Ideally, you should run some usability tests to figure out the bumps within your website. The tests don't need to be fancy. Just ask someone with fresh eyes to complete certain tasks (and ask them to verbalize their thoughts as they work toward that goal). Along the way, jot down any bumps or confusion that those users experience.
Afterward, you can use that guide to find specific tactics to overcome those bumps.
I am probably not going to be able to do all 125 on my site. What are the top 5 out of the 125 that you would recommend?