What kind of look do you want for your book? The justification that you choose will determine the look of your book. For history books there are two different justifications that look good, full or left. Full justification with both the left and right edges aligning straight up and down the page (like a newspaper column). Full justification will give your pages a clean orderly look but the spacing between words can sometimes look a little funny. With full justification, your headings could be either left, right, or centered on the page. Left justification has the left side aligned up and down and the right side is ragged. This gives a more conservative look to the book and the spacing between the words is consistent. If you have a book of poems, center justification will look great. The important thing is to choose one justification and stick to it. If you aren’t sure which way you want, look at a few different books to give you the feel of each style then choose the one you like best.