on Book Design made Simple:
Combining serif and sans serif fonts successfully can be a challenge, but it’s much easier once you know a few simple rules. It’s worth learning, as combining two fonts can really make your book design look professional. So don’t be daunted by the thousands of fonts available! The font-combining basics explained here will help to get you going quickly and easily.
When you’re experimenting with mixing fonts, you’ll see right away that some combinations work and others don’t. Below are some simple rules and examples you can use as a starting point.