You've got your amazing new cover! Now what?
It's time to create the best reading experience with the interior layout. A well-designed layout is an important aspect to keeping your readers interested - who enjoys reading a badly designed book? The best designs are the ones you don't notice. You want your readers blown away by the magic of your words, not that bad break and bad spacing.
Your interior design needs to match your book. You don't want closely spaced words in a small typeface on an easy read. Equally, you don't want a large, simple font on a serious work of non-fiction. Your proposed audience matters and getting it wrong could mean they put the book down and never pick it up again - and never pick up another from you. Getting it right leaves them enjoying your work and reaching for the next installment.
Remember those one-page essays your teachers used to assign that you didn't want to write? There was a fine line between writing SO BIG that they would mark you down or make you rewrite it properly and using nice big lettering to make it lovely and clear to read. Or the one-page essay that you desperately wanted to write and had to cram it all in, so you wrote in tiny, cramped letters and nobody could read the end result. It wouldn't have been an enjoyable experience for the teacher, and it's not for your book's readers either.