Font size is important in how easy a book is to read. If you make your font, say, size 14, you'll not only add a tremendous number of unnecessary pages to your book (and cost of production) but old will people love it. Balance that to your own (or your reader's) satisfaction Choose a font of no more than 12! Please. If you'd like to be popular with your publisher but you'd also like to try a new font to make your work easier to read, type a full line of text in Arial 11 and then right below it, compose the same line in your new font. Adjust the new font's size until the lines are roughly equal. But notice how long the line of text has become. Is it longer? Shorter? By how much? Endeavor to keep it within a few percent. Less than five? If it's longer, you turned your 300 page book into a 315 page book if the test line is 5% longer than Arial, size 11. Arial is pretty spaced out and easy to read but it has no serifs so it is fairly bland. Times New Roman was cool looking in the 1990s but has kind of died out. Garamond is a great font and easy to read except by the elderly. The letter shafts are very thin and the serifs are tiny, but enough to add a bit of almost unnoticed elegance to your words. It will also shrink your manuscript by a good 12% which is useful if you have a page limit for a writing contest/award, but not a word limit.