Very basic tips to "lockdown" your Android device. Obviously, the best recommendation would be to not use a phone at all, but realistically, in this day in age, that's not possible.
Ensure your Android device is on a supported version, and is always up to date.
Change your notification type to Hide sensitive notification content in your Android settings.
Use DNS66 to block your Android device from accessing malicious hosts.
Remove unused apps and factory installed bloatware using Android App settings on your device.
Some apps can't be uninstalled. In this case, you can force stop, disable them, then clean all app data and cache. This can all be found in the Android App Settings.