Certificate Transparency Logs
Your certs are leaking.
Credential Gathering
The art of Credential Gathering.
DNS Recon
DNS Recon, if you don't know where stuff is its gonna get hard to hack it.
E-Mail Gathering
If you know e-mail addresses you know naming conventions and possible even passwords.
Google Dorking
Ask the almight Google Machine. It. Knowns. All.
Identify Technologies
Who, What and Where.
public key disclosure
Sharing is caring, but this may be a but to much.
Shodan
And you though google knew a lot!