Start slow, and learn how to speak in non-pilot at first. Explain everything slowly and realize it will take 3 times longer to do when you're explaining, demonstrating and evaluating. Learn as many ways as possible to present the material because no two people learn in the same fashion and don't be afraid to ask advice of the more experienced instructors you work with. Also err on the side of caution. There is a fine line between intervening so soon that the student doesn't learn and letting a situation get out of control.
Time management is one of the hardest things when you start instructing. The rest will come to you as you go. The the person sitting to your left looks at you and says "what do I do now" is an eye opener.
Last but not least, have fun! To this day seeing a the light bulb click on in a student's brain is one of the most rewarding things I have done in my career. It never gets old.