Ignoring Meta Tags
It can be very easy to forget to create punchy, effective meta tags for your webpages, but without them you don’t control what users see in the Search Engine Results Pages (SERPs). This is detrimental to user experience and Google picks up on that. Also, duplicate meta tags are equally problematic: they make it hard for search engines to determine rankings between the two pages, much like duplicate webpage content. Always create meta tags and always compose them from scratch because rewriting (or, technically, patchwriting) can lead to not enough differentiation in the language.
Settling For Slow Page Load Speed
If Google has to wait too long for your page to load, you’re going to get penalized with lower rankings. Poorly written scripts, too many plugins, bloated code… there are many reasons for a slow page load speed. You may have the most beautiful webpage featuring sparkling copy and a fantastic call to action, but with a slow load you’ll lose both user attention and your chances for a higher ranking. It doesn’t matter how awesome your page is if nobody visits it.
Allowing Broken Internal Links
Google tests your links. If your page contains broken links, you’ll experience lower rankings in the SERPs. It may behoove you to periodically check your internal links to make sure they are all functional and relevant. Orphan pages are also detrimental. Orphan pages are pages of a website with no link leading to it. This makes it almost impossible for Google to find or crawl those pages and requires users to type in the URL directly… not an ideal user experience.
Believing That #1 Is Not Possible