Google's Security Checkup is a great way to verify the security of your account. This is great if you suspect unusual activity on your account, but it's also a good idea to do periodically as a preventative measure.
This checkup takes you through a number of steps. First it will verify that you have a current recovery phone number and email address along with security questions. Next, it will show you all of the devices that have accessed your account. It also tells you when those devices were connected, and the geographical location that each device accessed the account. This is valuable because if someone other than you had access to your account, you would know about it. You can say that everything looks good, or you can click "something looks wrong," which will prompt you to change the password. Lastly, Google Security Checkup will allow you to check your app passwords and two-step verification settings.