Advertising / Getting Eyes on Your Game

Hello everyone! I made this thread so people can discuss some ways to advertise their games! So if you have successfully sold your game, what are some ways that you were able to reach the public? What could a developer do in order to show off their game to potential buyers?

Essentially: What are some "surefire" (nothing is 100% foolproof) ways to reach more people? To get more eyes on your product? To get the public engaged and excited about the game you're developing, no matter which phase it's in?

Thoughts?