Social media can be a very effective tool for sharing your campaign, however if there’s one platform you use in particular, focus your efforts and attentions here rather than creating new accounts across lots of different platforms.
On Twitter, engage in conversations around topics and themes from your book, talk to people of influence and reputation who may RT (retweet) or endorse you, (get their attention by @’ing them directly) and where useful, use hashtags. Don’t be shy about tweeting regularly during the day, as so many tweets can easily get lost in the noise. You don’t need to post as frequently on Facebook, but use the lack of character restriction to your advantage. You can use Facebook for longer posts with photos, images, links etc.
Whichever platform you use, make sure you create content specifically for the platform you are using, i.e. don’t just copy and paste across many channels. And if you’re active on other platforms, such as LinkedIn, then use those too. But, by this stage, it may not be worth trying a new platform - getting a following on a new space might distract you from the real work at hand.
If you 'don't have time to be on social media all the time', don't worry. There are lots of free apps and plug-ins such as Buffer and Tweetdeck which let you schedule your posts in advance.