Free up space on your iOS device
21.05.12
We said at the outset that you shouldn’t start deleting apps at random when you need to free up space. Instead, you want to delete those apps you use the least, but take up the most space. And if you’re still at the General -> Usage section of the Settings app, your iOS device will make identifying those apps as simple as possible. In fact, the Usage screen lists all of your apps from largest to smallest. If you see, say, GarageBand or iMovie listed at the top—each of which gobbles up more than a gigabyte of storage space—and you never use those apps, now might be the time to bid them a fond farewell.
Remember that you can always reinstall those apps, should a need to use them arise. You can access your old, no-longer-installed apps from the App Store app on your iOS device, or using the iTunes application on your Mac (or PC, if that’s how you roll). On an iPad, tap the Purchased tab; on the iPhone, tap the Updates tab and then select Purchased. Then you can tap the Not On This Device tab to see a list of all the apps you don’t have installed, sorted by either name or installation date.
Source: Macworld (blog)