Disable microphone permissions to apps which are unnecessary especially when you use them for voice based search.
Facebook uses user data to display personalized ads based on the users search and web activity through "Off Facebook Activity" which can be found in settings under privacy.
To turn it off, first go to "Off facebook Activity" and clear history. In history you can see the history of all the searches, web activity and websites visited FB was tracking.
To permanently turn off, under the same section, go to "Manage your Off Facebook Activity" and turn off future activity.
The disable, the setting instructions are a bit confusing which take you through few steps. After reading the statements at each step you will finally reach the "turn off" button.
Let us know your experience after this :)