In order to save your data there are default settings within Facebook and Instagram that can be tweaked so video clips do not auto play and images on Instagram download in a smaller resolution. Open Facebook App More >> Settings >> Account Settings...
A great way to save cellular data is to ensure that you do not download new apps or update old apps when you are away from a Wi-Fi connection. The settings are easy to change and can be done via: Settings -> Cellular You then move the App Store slider to off (grey...