One of the winning features about iOS is that, even out of the box and without any tweaks, it's a really secure platform. There's rarely a shady app that makes it into the App Store, and Apple has struck the perfect balance between too much and too little security.
#1: Make sure you have a strong passcode
Don't be that person who's relying on 000000 or 123456 to protect their information. You are better than that. Much better.
Go to Settings > Face ID & Passcode (or Touch ID & Passcode on older iPhones), enter your existing passcode, and then tap on Passcode Options to get a set of options. Choose between Custom Alphanumeric Code (the most secure) or Custom Numeric Code (second-best option), or 4-Digit Numeric Code (I don't recommend this last option).
#2: Control leakage
Data leakage, that is.
Take control how much -- or how little -- information you want to be accessible on a locked device.
iOS 13 gives control over the following:
- Today View
- Notification Center
- Control Center
- Reply with Message
- Home Control
- Return Missed Call
- USB Accessories
I have everything disabled except for Home Control and Wallet.
The bottom line is that the more you lockdown, the more secure your device and data will be. The USB Accessories feature is especially useful because it will prevent the Lightning port being used to connect to any accessory if your iPhone or iPad has been locked for more than an hour.
Go to Settings > Face ID & Passcode (or Touch ID & Passcode on older iPhones), and enter your existing passcode to take control of this.
#3: Have you been naughty and been reusing passwords?
If you use the iCloud Keychain to store web passwords, you can now use this to check for password reuse (which is bad, so don't do it!).
Go to Settings > Passwords & Accounts > Website & App Passwords and authenticate with either Face ID/Touch ID or your passcode.
You will see a grey triangle with an exclamation mark next to any entry that is reused. To change the password, tap Change Password on Website.
#4: Reduce lock screen timeout to a minimum
The shorter you set the lock screen timeout setting (options are ranging from 30 seconds to never), the faster your iPhone or iPad display will require authentication to access it.
My advice -- never set it to never. Never!
You can change the auto-lock time by going to Settings > Display & Brightness > Auto-Lock.
#5: Hide notification previews
Prevent random snoopers from seeing your data by hiding notification previews.
Go to Settings > Notifications, then tap on Show Previews and choose When Unlocked.
Bonus tip #1
Reboot your iPhone every week or so. Not only will this improve performance, but it's also a simple way to protect yourself from remote exploits.
Bonus tip #2
Download and install iVerify.
iVerify is a security scanner that makes sure you are making use of the basic security features such as Face/Touch ID, Screen Lock, and are running the latest iOS version. It also runs a device scan that looks for security anomalies and gives you a heads up if something seems out of place.
The app also gives you a very -- and I mean very -- comprehensive list of tweaks and changes you can carry out to keep your device safe. Many of these are probably overkill for the average user, but for the power user or security-conscious, the app is a goldmine of information.
iVerify is not free -- it costs $2.99 -- but it's truly worth the money if you take security seriously. I know my way around iOS very well, and even I learned a few new things from going through all the guides contained in this app.