If you have your site built by a web developer, the font sizes, line spacing (leading) and other attributes should already be established. It’s best to stick with these conventions to maintain a clean, consistent appearance for your content.
Character Spacing — computer fonts are proportionally spaced. Unlike typewriters with mono (fixed) spacing, computer fonts (with a few exceptions) adjust spacing automatically, based on the context in which they are placed. It is for this reason, that a single space after punctuation at the end of a sentence is appropriate. Two spaces at the end of a sentence is a convention that was established with mono-spaced typewriter fonts. The result of using two spaces with proportional fonts is a river of white running down the page.
Line Spacing (Leading) — this is something you probably won’t adjust, but generally smaller type size on larger leading is more easily readable than large type on narrow leading.
Other Spacing — stick with the established convention for spacing before/after headings, paragraphs and other layout elements. This will give you a consistent, clean appearance to your site and minimize the possibility that it will become busy and disorganized over time as you continue to add content.
Emphasis — quotation marks (“) should be used when quoting something a person said. They should not be used to emphasize text. Instead use italics or bold attributes for emphasis. Underlining text is not advisable. It can make it look busy and more difficult to read and, on a website, it can easily be confused with hyperlinks.
Alignment — generally, the best text alignment is flush left, rag right. That is: aligned on the left side and allowed to wrap naturally on the right side. The flush left gives the reader’s eye a consistent place on the page to return to start the next line. Rag right is a visual cue for differentiating one line from the next. Newspapers often use full justification (flush on both sides), to make the most of limited space. It works reasonably well in the narrow newspaper columns, but can be difficult to read in wider layouts like a web page. Given that English is read left-to-right, flush right or center-aligned text is better used in specialized circumstances where the text is brief and presented more as a design element than text.
Column Width — columns that are too narrow or too wide are difficult to read. It’s best to keep column width in the approximate range of 10-20 words per line.