Type that is centred (ragged on both sides) doesn’t show the reader where sentences begin and end. It looks like each line is a sentence by itself.
	The layout that is easiest to read is type that has a straight left margin and a ragged (or unjustified) right margin.
	Long lines and bold type need more space between lines.

Appendix One — Six Graphics Guidelines — gives more detailed information about layout and design for clear writing.