First things first, you’ve got to be honest about which apps you do and don’t use. You might have a Snapchat account but do you actually use it? If the answer is no, delete the app as it’s wasting precious storage space.
Secondly, pretty much all smartphones have a menu within their settings where you can view how much memory/storage is being used up and by what. It’s worth reviewing this regularly, as you’ll probably be surprised by what you see. Apps like Facebook and Twitter can hoard huge amounts of space. Deleting and reinstalling them will clear out lots of unnecessary data whilst keeping all of your details and settings within the app. You also won’t have to pay to install the app again.
If you want to stop apps clogging up with data to begin with, limit the amount of time they have to do this. Head into your phone’s settings and turn off ‘background App Refresh’ for offending apps (the name varies slightly across devices but it will be similar to this). This will stop your apps from collecting information when you’re not using them. The only time they’ll use memory is while you’ve got the app open and you’re using it.