Code HTML Only - Don't go back and forth between HTML and CSS markup. Structure the page to make sense using as few DIVs as possible.
Modify CSS for phones - Stay out of the HTML and write CSS for viewing from a users phone.
Modify CSS for tablet - Again stay out of the HTML and see how far I can get with the design for tablet viewing.
Modify CSS for Desktop - Again stay out of the HTML and see how far I can get with the design for desktop viewing.
Modify HTML if need and corresponding CSS to finalize page.
Thanks to Mikael & Travis for helping me get so proficient here.