If you don't know who is Troy Hunt, then one thing to do right now is to signup for his great service: https://haveibeenpwned.com/

in essence, everytime(+) some massive break occurs, and your e-mail (and probably password) is among them after reaching "darknet" (meaning black market), you will get from haveibeenpwned an e-mail, urging you to some action (password change, account closure/change etc).

(+) Troy amassed over the years huge db of past breakins (so you can check your email presence also in past events) and with current respect/reputation he gots access to new ones pretty fast, informing you instantly in most cases.

Highly recommended.