Too Long; Didn't Read
Top Lesser Known HTML 5 & CSS 3 Tips and Best Practices: HTML5 and CSS3. Mouse events should have corresponding keyboard events. Image tags should have "width" and "height" attributes. The <html> element should provide the lang and/or xml:lang attribute in order to identify the default language of a document. <b> and <i> tags should be avoided and CSS should be used instead. Display the text bold in normal browsers. Display text bold when using screen readers.
Share Your Thoughts