1) Look up the suffix to your customers' zip codes on usps.com. In theory, the packages should get where they're going a little faster. Doing this should allow you to...
2) Use Media Mail for books, unless the book you're shipping is very lightweight, like a small trade paperback. When you're first getting your bearings, you can ask the postal worker to tell you the price for Media Mail, Priority, and First Class. After a while, you'll be able to tell which way to ship just by looking at a book. Don't mess around with cheaper shipping options on an expedited order.
3) Compare going prices for your item. You almost always want to set your price as the lowest. The exception is if one person is selling your book for $1 and everyone else is selling it for $15, you should sell it for $14. When the $1 copy sells, yours will be the cheapest. This is common sense, though.
4) Decide how much profit makes a sale worth the trip to the post office. If you're making a few cents, maybe it's better to throw the book in the donate pile.
5) Most heavy books will actually lose you money on Amazon, once you factor in shipping. Rare or otherwise expensive books are the exception.
6) You'll see a lot of sellers taking a loss on items in order to build positive feedback. This is a waste of time and money. Don't bother. The absence of feedback isn't a disadvantage in the Amazon community the way it is in places like eBay or Etsy.
7) Know when to give up. There comes a time when having crappy books taking up space in your home is not worth the possibility of future online profits. Donate the inventory that isn't moving. Maybe somebody else will like it more than you did.