Write the HTML code in a logical reading order
The writing order of the tags in the flow of the HTML code must follow the reading order of the page.
In other words, when one tag precedes another in the visual flow of the page, it must also immediately precede that element in the HTML code.
To test this rule, turn off the CSS and check that the resulting page order matches the page when CSS is active.
If some content is hidden by default, make sure that it is properly positioned in the HTML flow when styles are disabled.