Jks9199 makes some very valid points - especially about knowing your art and knowing how to teach it; many very fine martial artists never learn how to teach. Teaching requires that you not just know the techniques; you have to understand them, at a level that allows you to break techniques down into their smallest parts, teach those parts, and then teach your students how to recombine them. Along with that, you have to teach your students how to apply the techniques, singly and in combination, and how to modify those techniques for different situations.
If you want to teach a class in another facility, start checking into community centers, recreation centers, YMCAs, and athletic clubs. Many of them have outside instructors come in to teach anything from martial arts to aerobics to swimming to coaching a wide variety of sports. Be cautious about what the contract requires, and be sure you know what your compensation will be. For example, the YMCA I teach at starts new instructors at an hourly rate; once the class is established (if it becomes established) to the point that a percentage of the dues generates more income for the instructor than the hourly rate, they give you the option to switch over. Be sure you know beforehand if you are required to carry your own insurance, and if so, how much coverage you need, and what it will cost. Find out if you are going to be a regular employee or an independent contractor; there are advantages and disadvantages to both.
In the meantime, while you're training, take any opportunity you have to teach where you currently are. Find out if you like it, ask those you teach for feedback on what in your teaching style works and what doesn't, and being to develop your own style. Take notes on EVERYTHING - if you've ever wondered about it, or other students around you have wondered about it, chances are one of your students will wonder about it in the future. You're still going to miss things - but it's a place to start.
If you start an independent school or work for a facility as an independent contractor, talk to a tax professional; things you would never think of are deductible, and you need to know what they are so you can keep proper records.
Good luck with your training and your goals!