Once you go beyond 65 characters in a line, readers have great difficulty reading at their normal speed. You may want to switch to two columns or another layout that makes your document easy to read.
Justifying the right hand margin decreases readability because it causes the eye to stop at irregular spacing between words. Justifying means making the margins flush. This document has a justified left margin, and an unjustified, or ragged right margin.
It is very difficult to read sentences in all capital letters because it is unnatural and the normal visual cues are missing. A short header is readable in all caps, but anything more strains the reader. Consider these other methods to highlight important information: boxing the information, changing type size or font, using italics, or a light screen.
You increase readability by using headers that specifically describe the sections of your documents. Your reader absorbs information more quickly and easily, and understands its relationship to other information, if you use headers. The headers can then become a table of contents that communicates information more effectively to the reader.
If dense copy fills a page, you increase the chances that your reader will become discouraged. Give your reader a visual and mental break by using shorter paragraphs and headers.
Although cost may dictate how much white space you can use to open up your document and make it easier to read, make use of the white space you currently have. If you have a page where the text ends in the middle, ask yourself if you could have used a bigger type size and headers more effectively.