This is the checklist that I start with when I work with all my new digital marketing and consulting clients. It covers all the basics like fixing most of the common techinical errors most site owners have made and goes on to recommend some content strategy going forward.
Technical SEO Basics Checklist
htaccess 301 Redirects (www or non-www) - Set 301 redirects so your site resolves on either the www version or the non-www version of your domain, but not both.
Install Google Analytics - Make sure you have installed Google Analytics (or some alternative to Google Analytics), Google Webmaster Tools, and Bing Webmaster Tools on your site.
Short/Concise Page URLs - Ensure your page level url address strings are as short as possible and include the key words in them.
Site Speed - Ensure your site is optimized for quick load times (test this in the Google speed insights tool - https://developers.google.com/speed/pagespeed/insights). and pingdom
Fix broken links - Find and eliminate or cleanup any broken outbound links on your site using Xenu Link Sleuth.
Fix crawl errors in Webmaster Tools - Go into Google Webmaster Tools and cleanup/ resolve any existing crawl errors related to your site. The easiest way to do this is to place 301 redirects from the error path to the new path of that page.
Add an SSL Certificate - encrypting the connection to your website is now a factor that Google considers in its ranking algorithm. Websites with 'https' in the domain name prefix are encrypted.
Check/fix basic HTML tag structure, meta tags
Delete duplicate domains - and duplicate content or fix with htaccess 301 redirects
Social Media SEO Basics Checklist
Setup Social Media Accounts
- Google plus
Link accounts together - with buffer (for easy publishing)
Add images and meta data - to all social media accounts
On-Page SEO Basics Checklist
Create a blog (if not present) - you need a place to easily and regularly create fresh content
Remove duplicate and thin content
Perform basic keyword research - with the Google PPC keyword planner or Hittail. Use that research to decide what to write. Select a relevant longtail keywords, that will bring the right kind of prospective customers, and that your website can compete for.
Write a post/page that is compelling and adds value to your readers.
Use Post titles that have your key phrase in it and that is compelling to readers.
Include your key phrase in the H1 and/or H2 tag in the body of your copy.
Include keywords and phrases in the body - Be sure the words in your key phrase are present a few times in the body of your copy.
Tag your images - Ensure any images you use in your page/post are named with your key words where appropriate. Be sure to also include your key phrase in the alt tag where appropriate.
Use video to add value - Add video to blog posts wherever possible using Wistia. Google really likes it, since its more content rich, harder to make and fewer people are doing it.