Turn off your photo stream
Photo Stream combines all the images you’ve taken on your other devices with the photo roll on your phone, taking up precious MBs. Go to Settings > Photos & Camera, then switch off Photo Stream and revel in those sweet, sweet extra bytes.
Delete your old voicemails
Go to Phone > Voicemail > Edit, select old voicemails and Delete. Your phone still stores deleted voicemails for no good reason, so make sure that afterwards you scroll down to Deleted Messages > Clear All or all that hard work will have been for nothing.