I'm feeling feisty today so will (not without risk from blowback) go in the opposite direction from the tone set by the two respected (and kindly) posters above.
First of all, ThatOneSyrian, understand that you did not set the bar at your school and it's not your fault you have gotten a black belt and yet have little idea of how to go about learning to teach karate.
I will assume (hope?) you have at least 3 years experience in being taught karate. This is a good place to start. Did you not learn anything during this time? Did your instructor not ever correct you? Did he not ever explain anything to you? Did he not ever demonstrate technique to you? Did he not ever lay a kick into your ribs when your elbow was sticking up in guard? (Okay, maybe this last one is a little old school,... yet effective.)
My point is that you should have a good idea of how to teach (or not to) from the experience you already have as a student. This is the first place you should look to. Buka had some good ideas in this regard. You should also have confidence in your skills and a desire to help others learn the art. This I think, is about 90% of your answer. Don't overthink it too much.
The other 10% is creativity. The same kind you use in sparring. Try different techniques until you find what works on the guy in front of you. Read him. Come from different directions, vary the target, use hard and soft approaches.
For me, being a black belt means you have the skill, knowledge, and maturity to teach. Not just teach others, but to begin to learn to teach yourself. MA is a hands-on thing. Learn by doing and teach the same way.