Protecting Tax Information - Cyber-Security for the Tax Professional
Google Security Blog - New research: How effective is basic account hygiene at preventing hijacking May 17, 2019
Google Security Blog - New research: Understanding the root cause of account takeover November 9, 2017
Google Advanced Protection - Good demonstration of the trade-offs between convenience and security. Only go into this if you fully understand what limits it will put on you and you decide you really need it. You have been forewarned. That said, it definitely boosts the security of your Google Apps based accounts.
Paper on Account Hijacking - “My religious aunt asked why I was trying to sell her viagra”: Experiences with account hijacking 2014
Hardware Security Tokens
Yubikey - One of the best known options Used by Google in their long term program to protect their accounts prior to release of their own Titan product. Also available via Amazon and other sellers.
Google Titan - key advantage and downside is that it includes a key that works with Bluetooth. This may be your only option if your device cannot use USB connections nor NFC. Originally was the only option for iOS devices, though now Apple apparently allows these devices to use NFC on the phone.