Pick a Clean Design and Stick to It
Here the author (or whoever designed the layout) chose a typeface for the header that is nearly unreadable. This is a fancy typeface, meant for things like artsy newsletters, not a serious work of non-fiction. The words are spaced so close together that they are difficult to tell apart. The typeface itself clashes with the typeface used for the body text. A sans-serif typeface like Arial or Helvetica (which are nearly twins) would look much better.
The formatter used the same typeface for the chapter titles. This typeface looks to be one named “Broadway.” Regardless, it was a very poor choice for this book.
Notice how much better the header would look in a typeface like Arial in an 18-point bold font:
As I pointed out in a previous blog, the best typefaces are those that work well together. You can select a typeface that complements the body text, which is normally a serif typeface such as Times Roman, Palatino, or Garamond, from the sans-serif typefaces that are available to you. You can set chapter titles, headers, and page numbers, in the same sans-serif typeface, with headers and page numbers in one point size and chapter titles in a larger point size so they stand out. You can also use a different typeface for the chapter titles if you wish. There are no hard and fast rules; just be sure the typefaces you pick look good together.
In many non-fiction books, you may also need to have subheadings. You can set these in the same typeface as the page headers, normally in a slightly larger font. You can also set them a slightly different sans-serif typeface, just so long as it goes well with the one used in the headers.
Here is a page from a well-formatted book, First to Die: The Tragic Loss of the SS Vestris:
The header and page number are 11-point Calibri; the subheading is 13-point Calibri; and the body text is 11-point Georgia. Note that the first paragraph under a subheading has no first-line indent. This is standard book formatting.
The authors used 15-point leading throughout (leading: the space between lines of text; rhymes with sledding).
To get a good feel for the art of formatting books and other publications, look at ones that are commercially published—avoiding those like the top example, which are a distinct—and ugly—minority. You are sure to pick up a good feel for this sort of thing if you study enough published books, looking at the formatting instead of reading the words.