Contrast and Emphasis
Good designs generally have good contrasts and emphasis between different elements. Contrast creates a visual hierarchy and lets us emphasize certain elements over others. The title is one example, and so are the highlights or quotes sprinkled over those long-form articles.
Good contrast between elements helps guide the reader through the content, whereas having good color contrast between the text and the background helps improve readability and make the design more aesthetically pleasing.
There are several ways of improving contrast, and the most obvious is by using bigger font sizes and thicker font weights. The less obvious is to reduce the contrast of the surrounding elements so the element we want to emphasize stands out more.
For example, use a lighter shade of gray for the caption so it doesn't draw the reader's attention as much. Icons, accent colors, and whitespace are also tools for improving contrast.
Perhaps the quickest way to make a good design is to iterate a lot. Design is way more of an art than a science, so keep at it until you develop your own sense of style and taste.