With only 140 character?
Guess what the promotion tool at Twitter is.
The post includes examples of the hashtags you want to use with samples of how to use them. It has where to upload your cover; how to promote a sale; and, even has a link to 200 more promotional hashtags.
Panzer says, "I never knew there were all those hashtags for writing."
If you're looking for information on book promotion on Twitter, tootle over to twitter for book promotion