This guest article from Dana Lynn Smith is part of the virtual book tour for her new book, The Savvy Book Marketer’s Guide to Successful Social Marketing.
Twitter contests and giveaways are a fun way to build buzz, increase your followers, and promote your book at the same time.
With a prize drawing, a winner is drawn from the contest entrants. You can give away a free copy of your book or put together a prize package that includes several related books or products. One advantage to inviting others to contribute to the prize package is that they can help promote the contest. You may want to create a web page or blog post that describes the contest, so you can link to it.
Typically, people enter a Twitter contest by following you and then re-tweeting a specific message such as this: “Just entered to win an autographed book: The Garden of the Soul. Just follow @LynnSerafinn & Retweet. See http://bit.ly/beq28 #GOTS”
Tweet and Re-tweet
You get the promotional ball rolling by tweeting about your contest, then others pass the message on for you by re-tweeting.
You can keep track of the entries by searching Twitter to locate the re-tweets. Another idea is to add a unique hastag, such as #GOTS in the example above, to your message. Then you can search Twitter for the hashtag to bring up a list of your entries.  Make sure no one is already using your hashtag by searching for the hashtag on the Twitter search page. http://search.twitter.com It’s a good idea to copy or print out your entries each day, to make sure you don’t lose any.
Make it random
An easy way to select a winner is to generate a random number at http://www.random.org. For example, if you have 224 entries, this free service will generate a random number between 1 and 224. If your number is 53, then count down to the 53rd entrant to find the winner.

Another option is to use a free service like TwiveAway http://www.twiveaway.com/ that automatically keeps track of entries and selects the contest winner.
The optimal length of time for a contest is about seven to ten days. If it goes on too long, people may lose interest and get tired of seeing the promotional tweets.
Let people know what happened
At the close of the contest, notify the winner and then announce the winner publicly by tweeting about it or even sending all the entrants a direct message.
With a giveaway promotion, everyone who enters receives a gift, such as a free ebook.  You could direct people to a web page where they fill out an opt-in form and the free ebook is delivered instantly though an autoresponder service such as Aweber.   https://www.aweber.com
Another option is to use the free service at TwiveAway http://www.twiveaway.com/to deliver a downloadable product to everyone who signs up.
You could also combine these two types of promotions by giving everyone a gift, then holding a drawing for the grand prize.
Before you begin your Twitter contest, make a note of the number of followers you have and compare it to the number at the end of the contest.
Dana Lynn Smith is a book marketing coach and author of The Savvy Book Marketer Guides. One of her recent releases is The Savvy Book Marketer Guide to Successful Social Marketing