Conducting Effective Twitter Contests, by Tony Eldridge, offers some great tips on how to grow your following with Twitter contests. Having a large number of people following you can increase your chances of marketing effectively with Twitter.
This Kindle book is not written to teach you how to use Twitter, nor to teach best practices, though it does indicate that you should not use contests to sell something directly. Contests are intended to create excitement among people who are likely to have an interest in the product or service you offer in order to entice them to follow you. Once they follow your tweets, you can then establish a relationship with them. That's when the selling can begin, because effective selling is based on establishing a relationship.
One thing that makes this book a great learning tool is that it contains links to a series of how-to videos, each produced specifically for this book. Between them and the text of the book, you will have plenty of great information with which to plan and launch a successful contest, that can bring you more followers.
If you have a product or service that you want to offer people, this book is a great value. It is also useful for authors. I highly recommend this book, especially because it's currently only $.99.