A big chunk of game design does not actually involve designing any game parts, but rather the best way of presenting it. Some of it needs other people to step in (illustrators and editors, mostly) but there's another element that is crucial and you need to work it out: Text presentation. By that I don't mean choosing the right words to express something (that's for your editor to worry about) but rather choosing the right look for your words.
This is relevant because I spent several days fixing issues that came up when I talked with a local printer. The issue is more complex than it seems, even though I was already familiar with a lot of prerequisites, I still missed some. You don't see a lot of discussion about this aspect of game design so I figured I'd offer my experience and thoughts on the subject.
Put on a Happy Typeface
Characters (the symbols, not the fictional people) are the atoms of writing. And one of the most subtly important steps of proper presentation is to choose the right typefaces and fonts for your text. But first a clarification: A typeface is not the same thing as a font, rather, fonts are individual styles of typeface. Verdana is a Typeface, but Verdana Bold is a font. I call typefaces fonts all the time in everyday talk, but this is one of those instances where the difference matters. And now that we all have learned something of mild usefulness we can move on.
Your typefaces must fit your style. Sometimes the best way to explain something quickly is with an example, and I am going to use a controversial one: Comic Sans is actually a pretty decent typeface, it just doesn't go well with anything you want to be taken seriously. It looks super goofy and cartoony and yet people use it for their Linkin Park AMVs made with Windows Movie Maker and I have no idea what they're thinking. There are hundreds of thousands of typefaces out there for pretty much any style you can think of, you have to find one that works. Don't just use Times New Roman and Arial for everything, because you are missing out.
Your typefaces must be comfortable to read. Times New Roman and Arial work with eveything partly because they are solid typefaces and partly because we are so used to seeing them everywhere our brains already recognize the words written with them automatically. Point is: The more distinctive and unique your typeface is, the harder it is to read and the slower the text is to digest. Fancy fonts make cool headers and titles, but are terrible for reading full sentences.
Balance serif typefaces with sans serif typefaces. There is some research indicating that typefaces with the pointy ends (the serifs) to be easier to read on printed paper, while the reverse is true for sans serif typefaces and text on a screen. Honestly a lot of it is ambiguous and highly subjective so I don't particularly subscribe to the idea, but it bears keeping in mind. I personally find serif typefaces to be an overdesigned blight on my eyes, but sans serif fonts annoy a lot of other people so I try not to go overboard with them. What I get out of this is that you need to use them both. My method of choice is to use headers in sans serif and body text with small serifs.
The less typefaces, the merrier. Good design is as little design as possible, and that extends to the number of typefaces you should use. All your headers should have the same typeface, as should all your tables, and basically everything you can think of. You do this because you want readers to recognize the parts of the text that interest them the most immediately, and also because you don't want your text to read like a ransom letter. Distinctive, unique sections can have their own typefaces if you want them to stand out, but for the most part you want to have no more than three or at most four typefaces per page: Chapter Header, Paragraph Header, Body Text and Table Text.
Get the Layout of the Land
Ease of use beats fancy visuals. If you can fit a whole section of rules text in one page or can split it into two pages with some art in the middle, you should do the former. Games are meant to be played. I'm going to care a lot less about how pretty your book is when you make me flip back and forth between 10 pages just to check out the descriptions of the weapons in your huge weapons table.
Mind your Margins. Margins are not a problem as long as you are working with just .pdf files, but
they become very important if you want to print things out. You don't
want to accidentally have large chunks of text missing, after all. The
amount varies depending on page size and publication type, which is why
you ought to figure out both of those before you commit to writing
anything. Hardcovers need more inner margin space, color books need a
sizable gutter and bleed. There are too many variables to list, really.
Backgrounds are nice but they should be unobtrusive. People
have been reading black text on white backgrounds for hours at a time
since forever without any significant problems, but now there's this
trend where RPGs need to have the text on a background with pretty colors and
give their sidebars ornate borders and so on and so forth. Sometimes
this is helpful, but the grand majority of the time it doesn't add
anything and only gets in the way.
Don't be afraid of splitting text into columns. If you need to write many short text blocks with short sentences in your page, you should split it into columns because you can fit more text in one page that way. I could fit 10 weapons in one page by using two columns, or I could fit six without columns. It is a matter of practicality. Don't use them if you don't need them though, and you should not have more than two, or text will be too small to read at a glance. Newspapers get away with it because you're supposed to take your time with them.
In my case I had to change the body text typeface and make a few extra milimeters of space in each margin. This may not sound like much, but I had to basically go over every page readjusting the columns and making sure the text still fit within its borders, because the same characters have different lengths depending on their typefaces.
It got so troublesome that I decided the book interior will only be in black and white. I already have some things in color but the requisites to do something good in color would require me to cut on text or increase pagecount considerably. The positive side of this is that it'll be cheaper for everyone involved.
It basically took two weeks and the better half of a third but that hurdle has now been solved.