The University of Toronto’s Writing Centre has a thorough set of Tools and Rules to Improve Your Spelling.
Similarly, the University of Ottawa’s Writing Centre has a page with some spelling basics and further links to explore.
Check out the Top Ten Spelling Rules at Howtospell.co.uk, and explore their links and videos.
The Oatmeal offers a helpful guide to 10 Words You Need to Stop Misspelling.
The Logic of English teaches 31 rules for spelling in English.
Dyslexia.org offers an extensive look at spelling rules.
The Riggs Institute outlines 28 Rules for English Spelling.
Howcast breaks down the basics in 2 minutes in its video How to Learn the Basic Spelling Rules of English.