@Sadia-Din
I have an android phone but essentially your data tracker works the same as does your data saver. Make sure you enable both and turn off your wifi assist. I reset my data tracker at renewal once I see my data reset in my account (about midnite et.) I set my data warning at 25% of my data and the limiter at 50%. This way if an app goes crazy I get plenty of warning before it can chew thru 5 gb or more ( it saved me from doing that last month!)
After setting up those tools in your phone go to your mobile data usage for the list of all of your apps. Turn off all of your background data. If you can turn it off you don't need it. This can save you up to 38% of your data. Periodically check these as sometimes they turn back on?!! Remember to turn SMS/MMS on as unlike iMessage they don't use your plan data.
Welcome to public mobile!
BTW.... don't do a speed test in the first 48 hours until your 4G LTE data is throttled down to 3mbps otherwise you can use up to 500mb performing just one test.