It may seem a little odd to set a schedule for something as casual as Facebook or Twitter, but if you’re using social media as a professional author, you need to be diligent about it. Remember: this is a part of your job now.
It’s a good idea to update your blog, if you have one, ever week or every other week, to keep readers coming back. If you’re keeping a static website, it’s a good idea to go review your site monthly to make sure all the information is up to date, especially if you have any ongoing events or tours.
For sites like Facebook and Twitter, you of course update whenever you have something note-worthy to share (news about your next book, your tour schedule, or you new blog post, for example), but you should be interacting between updates as well. With Facebook, every few days is best, but twice a week is a good minimum. With Twitter, the more the better really, but I advise aiming for at least one interaction a day; it can be an original tweet or a retweet, but it’s important that you keep yourself visible.
This may sound a little overwhelming, but you don’t need to schedule social media time every day. Using sites like Hootsuite and apps like Tweetdeck, you can set up tweets and Facebook updates ahead of time. You can designate a few hours on a specific day each week, and spend that time creating the updates for the week ahead. Of course, you can always pop your head in during the week to actively participate, but you don’t need to feel like you have to be constantly online.