You are very welcome. I usually clear cache before I quit an app. Some apps provide the option to clear cache in the app. To empty Safari's cache, go to Settings - Safari, and tap Clear History and Website Data.
You can also find on the internet many other similar things you can do, like deleting unwanted apps, messages, offline content, downloaded podcasts, and so on.
I just knew a trick to let the system clear cache automatically, but it only works when your available storage is less than 2 GB. Here is how: go to App Store, find an app that is bigger than 2 GB, tap to download it. Then the system will remind you that you can not download the app because you don't have enough storage. Tap OK and the system will start to clear cache automatically. Don't worry if the storage reminder doesn't show up. The system will still clear cache while the app is downloading. After downloading you just need to delete the app. Then you will gain 1 to 3 GB storage. It depends.