Windows/Mac: Your iOS device has a limited amount of storage. It can store a lot of junk you don't need over time, such as temp files, scripts and failed sync files. PhoneClean is an app that deletes all that junk for you.
All you need to do is launch PhoneClean, attach your iOS device to your computer, and click the "Start Scan" button. PhoneClean will dig through your device and give you a report on what it can safely delete. Check the boxes for the junk you want to delete. I didn't reclaim much space myself, but your mileage may vary.