With a solid plan beside you, you can start to code a template (or prototype) page. This will be a single page in your site and will act as the basic template for your other pages. Establish the structure of the page and clearly comment where your navigation, main content, page heading, footer and so forth are coded.
Use appropriate structural tags to describe your content. Put each paragraph of text in <p> tags, put headings in the appropriate level of heading tag and so forth.
Now validate this template page.
When your code is valid and you are satisfied with the general structure, you will evaluate your template. Return to construction once you have perfected this initial page.