When setting margins in Word for a paperback novel, there are several factors to consider. Generally, the margins should be wide enough to make the text look balanced on the page. A margin of around 1 inch all around (top, bottom, left, and right) is a common choice. But if you anticipate your book having a thick spine, you might increase the left margin slightly, say to 1.2 inches. Also, some people like to have a bit more white space at the bottom, so they could set the bottom margin to 1.1 inches. It really depends on your aesthetic preference and the overall look you want for your paperback novel. And don't forget to preview how it will look when printed to make sure the margins are just right.
Typically, for a paperback novel in Word, you might want to use 1-inch margins on all sides. This gives a clean and professional look while also allowing enough space for binding if the manuscript is printed and bound.