How to code in HTML and CSS, really?

Update on February 22, 2013
Let’s get to the details on how to write the HTML markup, really.

1. Write pure text of everything
2. Enclose all texts in semantic HTML tags — don’t use <div> and <span>
3. Add lists — <ul>, <ol>
4. Add headings — use only <h1>
5. Add sectioning elements like <header>, <nav>, <section>
6. Check document outline

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HTML (weighing on content structure and document outline)

1. Write HTML5 tags
2. No <div>s, no <span>s
3. Check if HTML elements are sematic
4. Check document outline
5. Use <div>s and <span>s for visual design-specific purposes

CSS (weighing on mobile-first layout)

1. Write styles
2. No floats
3. No positions
4. Set color and background-color
5. Set images
6. Looks good on small devices? Move on to the next size