Selected answers from the Dumb SEO Questions G+ community.
Jason Mun: Grab your list of urls from your xml sitemap (if you have one) find and replace https:// with http://. Whack that list of urls in to Screaming Frog in list mode. Export redirect chains report.
Yuliana Kronrod: Also check how www vs non-www version redirect. To enable hsts preload, you’ll need non-www to go directly to https non-www before adding the sub domain (if used for your site): check status here https://hstspreload.org/
Yuliana Kronrod: Validate canonical tags, social tags, urls in sitemaps, internal links (if any absolute links exit) to html pages and images - all can be done in Screaming Frog
David Iwanow: Ah semrush have a great site audit tool that exposes a lot of common issues... Also look at your http and https Google search console indexation reports and search analytics impressions/clicks... Old http site should have mostly dropped off and moved to https