Stop using 4 digit numeric passwords on your phone

a 4-digit numeric passcode would only take 34 minutes to brute force, while an 8 digit alphanumeric passcode would still take over a million years

Source: [FREE] Apple Versus the FBI, Understanding iPhone Encryption, The Risks for Apple and Encryption – Stratechery by Ben Thompson

This is a very good read on Apple’s fight with the FBI over what are appropriate measures to access data on an alleged terrorist’s phone.