You don't even need RCs to become lucid, they are ultimately just a test to see if you're dreaming or not. Get into the mindset to lucid dream - you could be dreaming right now, but how do you really know for sure until you test? Notice how the keyboard feels as you type, and notice how gravity is acting on you, and how you won't be able to get up off the chair unless you put in some effort. It's the small things like this that allow one to become aware in a dream.

For that RC, it's really just seeing if you can breathe - I don't close my mouth while I do it, but some people do.