Serif connotes formality and readability in large amount of texts.
Sans serif brings a clean or minimalist look to the text.
Slab Serif carries a solid or heavy look to text.
Display or Decorative caters to a wide variety of emotions or themes.
Design Principles and Elements: the principles in designing text elements are Emphasis, Appropriateness, Proximity, Alignment, Organization, Repetition and Contrast.
Emphasis refers to the importance or value given to a part of the text-based content. When trying to make a point or highlighting a message, you can make the text bold, italicized, have a heavier weight, darkened or lightened (depending on your background color) or enlarged.
Appropriateness refers to how fitting or suitable the text is used for a specific audience, purpose or event. In the creation of text-based content, make sure that the selection criteria (tone, style, purpose, clarity) is followed.
Proximity refers to how near or how far are the text elements from each other.
Alignment refers to how the text is positioned in the page. This can be left, right, center or justified.
Organization refers to a conscious effort to organize the different text elements in a page.
Repetition concerns consistency of elements and the unity of the entire design.
Contrast creates visual interest to text elements. (light and dark, large and small, etc.)