QUOTE: “Returning a code other than 404 or 410 for a non-existent page (or redirecting users to another page, such as the homepage, instead of returning a 404) can be problematic. Firstly, it tells search engines that there’s a real page at that URL. As a result, that URL may be crawled and its content indexed. Because of the time Googlebot spends on non-existent pages, your unique URLs may not be discovered as quickly or visited as frequently and your site’s crawl coverage may be impacted (also, you probably don’t want your site to rank well for the search query” GOOGLE
Google recommends that all websites use https:// when possible. The hostname is where your website is hosted, commonly using the same domain name that you'd use for email. Google differentiates between the "www" and "non-www" version (for example, "www.example.com" or just "example.com"). When adding your website to Search Console, we recommend adding both http:// and https:// versions, as well as the "www" and "non-www" versions.
The basics of GOOD SEO hasn’t changed for years – though effectiveness of particular elements has certainly narrowed or changed in type of usefulness – you should still be focusing on building a simple site using VERY simple SEO best practices – don’t sweat the small stuff, while all-the-time paying attention to the important stuff  – add plenty of unique PAGE TITLES and plenty of new ORIGINAL CONTENT. Understand how Google SEES your website. CRAWL it, like Google does, with (for example) Screaming Frog SEO spider, and fix malformed links or things that result in server errors (500), broken links (400+) and unnecessary redirects (300+). Each page you want in Google should serve a 200 OK header message.
At first glance, the Ads or SC appear to be MC. Some users may interact with Ads or SC, believing that the Ads or SC is the MC.Ads appear to be SC (links) where the user would expect that clicking the link will take them to another page within the same website, but actually take them to a different website. Some users may feel surprised or confused when clicking SC or links that go to a page on a completely different website.
QUOTE: “Ultimately, you just want to have a really great site people love. I know it sounds like a cliché, but almost [all of] what we are looking for is surely what users are looking for. A site with content that users love – let’s say they interact with content in some way – that will help you in ranking in general, not with Panda. Pruning is not a good idea because with Panda, I don’t think it will ever help mainly because you are very likely to get Panda penalized – Pandalized – because of low-quality content…content that’s actually ranking shouldn’t perhaps rank that well. Let’s say you figure out if you put 10,000 times the word “pony” on your page, you rank better for all queries. What Panda does is disregard the advantage you figure out, so you fall back where you started. I don’t think you are removing content from the site with potential to rank – you have the potential to go further down if you remove that content. I would spend resources on improving content, or, if you don’t have the means to save that content, just leave it there. Ultimately people want good sites. They don’t want empty pages and crappy content. Ultimately that’s your goal – it’s created for your users.” Gary Illyes, Google 2017

Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.