Fonts or, more properly, typefaces, may not be a major concern for writers but it is certainly useful to know a little about them. For those of us who also design books – for ourselves or others – the subject is of greater importance.
Many authors are quite willing to leave it up to their publisher or designer, but for publication purposes, it is pretty safe to say 'when in doubt, use Garamond.' That is, utilize some variant on the Garamond typeface for novels and other fiction; it is not necessarily a great choice for poetry or nonfiction or magazines, but it can always work. I'll get back to that.
But first, I wish to touch on fonts used for the actual writing process. Assuming one uses a word processing program on a computer (there are a few holdouts, I know), what would be a good choice? There are two concerns with any typeface, readability and legibility. These are not necessarily the same thing.
Garamond is very readable. It pulls the eye right along a line of text. This is great in a book but not so good for thoughtful editing. We need to be able to slow down and see everything clearly.
Now, for poetry or songwriting, I prefer to use a monospaced font. This makes it easier for me to show the rhythm of the piece, line up the accents and breaks in the text. And to make it simple to exchange song lyric files with other musicians and have everything show up in the right place, I use the ubiquitous Courier New. Of course, Courier is also pretty much the standard for screenplays, if one is inclined to their creation.
Courier is obviously not suited to publishing poetry, however. Nor would I use Garamond, as a rule, preferring something that makes the eye linger rather than speed-read! Still, it should be a good readable typeface, not something intended for display. I might be inclined to say 'when in doubt, use Palatino' here. It has, perhaps, been overused but it always works.
Not for novels, however — I actually laid out my first novel, the YA title THE MIDDLE OF NOWHERE, in a variant of Palatino. That would be URW Palladio, from the same designer (Herman Zapf) who created Palatino. I would not use it again but it is not that big a deal. It still works well enough.
I also use Palladio for writing. It is legible on the screen, and easy to work with both in the writing and editing phases. That is just my personal choice; there are plenty of other good on-screen fonts. Georgia should be excellent for writing, as should some of the newer 'standards' that Microsoft has included in recent versions of Windows. But use something that is not cramped. Avoid Times New Roman and similar fonts intended for newspaper and magazine use. They work better in narrow columns, not in lines extending across a page. Your eyes will thank you.
That is equally true in a publishing context. I will admit that my very first chapbook of poetry, PIECES OF THE MOON, originally appeared set in Times NR. It didn't look that bad, admittedly, but I eventually replaced it with Gentium. This, likewise, is something of a magazine-oriented font but I chose it because it required minimal change to the layout. At least, I got away from that too-familiar appearance of Times.
Occasionally, that Times New Roman is needed, however. If one is submitting printed-out work to a publisher, it might be specified. That shouldn't matter, of course, in a digital file. I also prepare my files intended for EPUB in Times, simply because it always converts without any problems — and the reader can choose whatever typeface they desire, anyway.
Speaking of files, some publishers may insist on Microsoft Word for submissions. I refuse to use it on general principle. I work almost entirely in Open Office Writer (Libre Office is just as good), sometimes even laying out the final book there. I used to prefer Corel WordPerfect and will admit it does have some functionality advantages. But back to fonts.
And back to Garamond. My recent “Malvern” novels (COAST OF SPEARS and the soon-to-be-released VALLEY OF VISIONS) are set in URW Garamond No8. This, as the afore-mentioned Palladio, is part of the group of typefaces URW donated to the GhostScript project some time back and are completely free to use. A recommended download for anyone wanting a group of very usable, no-strings fonts (and part of the Scribus free desktop publishing program download).
There are any number of other good Garamonds out there, some free to use, some not. Look around. And there are Caslons and Baskervilles and so on, all of them perfectly adequate. If you are designing your own (or, again, someone else's) book, you'll want to give them some study. Or, when in doubt, use Garamond.