There are many ways to get people onto your list. Lead magnets are one such resource. For example, you can build ebooks, checklists and cheat sheets. But you can also do content upgrades, such as PDF versions of an article with added resources in them, four-part video training series, and more. Think about your audience and what you can offer them to better serve them, then treat them with some respect and you'll eventually reap the rewards.
Hunt for under-priced used books that you can sell online. Download an app that reads ISBN numbers so you can scan the barcodes on books. This will pull up the book’s current price on Amazon so you can see if it’s worth trying to resell it. Then, visit used book stores, thrift stores, and garage sales to look for high value books. Post the books for sale online using sites like Amazon or Ebay.