I had a disagreement with Facebook on their stupid policy regarding the amount of text allowed in an advertising poster which led to some research and a useful discovery.
As I have previously stated, if you advertise with FB you should only target your book page, be it Amazon or whoever you use. You can use this to get 'Likes' for your FB page like some attention hungry teenager, but as an author you will go hungry, literally. 'Likes' do not pay the bills.
Go on to FB and search 'Advertise on Facebook', this will link you to the process. Target your countries and audience carefully, do not 'shotgun-and-hope-for-the-best
IGNORE the option to post your advert in the newsfeed but SELECT 'Right hand column' as this is where 80% of 'clicks' to my Amazon page originated.
I only advertised for seven days and it cost me $50 to reach 209,566 members and I received an average 170 daily clicks to my Amazon page. Whether anyone actually bought a book remains to be seen, but there you have it. The right hand column ads work much better than news feed ads.
Of course, you need to post an eye catching ad too, but I can't help you there.
Best of luck