I’ve found an older article on reading patterns which I think is still quite relevant. It states that a user reading web content typically reads in an F-shaped pattern, with long and short horizontal sweeps along headers and vertical scans down the left margin (the article illustrates this with heat maps on various web pages).
Quote from the article:
Users won’t read your text thoroughly in a word-by-word manner. Exhaustive reading is rare, especially when prospective customers are conducting their initial research to compile a shortlist of vendors. Yes, some people will read more, but most won’t.
This F-shaped reading pattern reminds me of the inverted pyramid style of writing. Layouts, spacing and pictures can benefit or obstruct this reading pattern. One thing I like to do is inject whitespace and images into blocks of text, which helps to make the content seem less dense and easier to scan and pick out keywords.