Font Forum

Is there a standard word spacing (e.g., triple the letter spacing) that I can use as a starting point?
thx

It really depends on the particular font. As a general rule, the darker the color, the smaller a word space should be, as large spaces will put white gaps in the page. Condensed fonts should have spaces that are proportionally larger compared to the characters, as opposed to smaller proportional spaces in a wide font. You need to really understand how your font works: test a paragraph at 8pt, 10pt, 12pt, and 16pt with spaces that range from 1/10th of an em, all the way up to 1 1/2 x em - some of them will instantly be wrong, and you don't even have to print it out. Whittle it down, then start really looking at how it works in context with different characters. You may find that certain advance widths work really well with round characters, but they leave your punctuation-to-caps space in bad shape. Eventually, you will find a good middle ground space that you like. Go with it. Most importantly, nothing works better than knowing your own font.

Microsoft Typography — Design Standards is a useful site to bookmark.