ITS vs. IT’S is tricky because the way to use ITS goes against everything we’re taught about possession. Here’s a quick explanation that I hope will clear up the confusion:
When something belongs to someone or something (possession), we normally use an apostrophe:
However, when something belongs to IT (or is from IT), no apostrophe is needed:
IT’S is used as contraction for IT IS or IT HAS:
See the difference? Given that ITS is an exception to the rule of possession, it really comes down to memorization to get it right. But it’s important! I do a lot of reading about publishing, and as a result I often find myself checking out author websites and Amazon pages, which include anything from bios and book descriptions to blogs and Twitter posts. While that content is entirely separate from what’s contained inside the pages of an author’s book(s), if I see errors such as getting its/it’s wrong, it affects my opinion of that person’s writing.
As I’ve said in this space many times, if you’re going to present yourself as a professional writer, make sure ALL your writing looks professional, not just what goes inside your book. Everyone makes mistakes, and sometimes a quick proofread is all it takes to catch them.