Facebook privacy is biggest issue of times and people direly look for solution which can make their profiles safe, which lies in the Facebook itself.
The Golden rule to privacy is do not add people you don’t know in your contact even if they appear in the list of your Friends list. This will make your content very inaccessible.
Once you are harassed, block the person who did this and try not to add people which appear in your friend request right after this with fake profiles.
As it is said try to think twice what you say, similarly try to think thrice what you post. It helps in gathering audience that are relevant and filters out the trash. Do not spread hate word for any minority or majority in your profile, group and page that instigate fire and try to hack of disrupt your reputation on Facebook.
Share the post privately also that had content which is close to your personal or social life.
Keep on checking old posts, if they lose their privacy settings, also keep on checking new one whether they are retaining or not.
Hide you private information like, number, e-mail and home address on Facebook.