Make your own collection of old and rare books. Start by contacting your local library. Libraries will sometimes sell old books. Many of these books can be bought for 50 cents or less. Checking the dates and qualities of the books may take longer, but you may get a better specific collection. Books that were published before 1900 and are still in fair condition are usually worth getting. They will sometimes be worth 10 or more times what you bought them for. Also check local estate sales, auctions, fire sales or flea markets.
Find out the going rate for your books. Use Internet search engines you are comfortable with to find book collector websites. There will be numerous rare book dealers who have lists you can look over. If any of your books are listed, you can find out how much the book is going for. Some of these websites will have their own built in search engines that you can use to look for a specific book. If you cannot find the price for all of your books, the library will often have pricing guides for rare books. Make sure you get the most recent edition of the guide.
Put your books up for sale. Having a yard sale will probably only fetch as much money as you paid for the book, not as much as it is worth. It is best to take the books that you know are worth something, take pictures of them, and post them on your favorite e-commerce website. Any site like eBay.com will work. Make sure you post closeup pictures of your books, from all angles, to show their quality. These websites will also allow you to take credit card payments, which will ensure you get your money quickly.
Keep trying. Remember, other people may be selling the same book as you for a lower price. Once that seller's book is sold, there will still be a need for the book. Once all other sellers have sold their copies of the book, yours will be in demand,
Continue selling. Don't stop once you start. Certain e-commerce sites will give you a better rating as you sell more and more books. Eventually, you can get a high rating on your e-commerce site and start your own e-store on the website. You are more likely to sell rare books if people trust that they are getting quality books from you, so make sure they are.