I think sharing through social media definitely has a great impact to increase the visibility of a website. Not necessarily improving the SEO of the page directly (because social links are generally nofollow) but it will definitely help to attract more visitors and when those visitors share your content, they may even do so on their personal sites with a 'dofollow' link.

Creating long tail keywords - this is great and one of the things I emphasise quite a bit on with my clients. It's not always about aiming for that #1 dominating keyword which every giant in the industry wants to rank for - sometimes picking up lots of little wins instead of playing the lottery for the big win can prove to be much more rewarding ;)

If you get a chance, check out my extensive write up on Optimising My Steemit Blog Posts.

Keep steemin' :)