There are known ways for saving data such as using a browser that compresses data on websites.
Also switching on play store apps to only update on WiFi or manually updating them when you have a WiFi network.
Using WiFi the obvious one when out so not using providers data.
And a new one I have discovered called datally from Google that restricts apps updating in background so saving data.
Plus they have a couple of clever ideas up there sleeves such as setting up a daily limit you set yourself that one you use up blocks you from using data tool next day.
An emergency bank were you can set aside a certain amount of data from being used and can access in emergency.