In my limited experience as a FI always liked to keep things simple.
The whiteboard, large enough to write clearly and separate your sections with a selection of markers is a great tool. Just don't overcrowd it with unnecessary information or complex diagrams - use a handout.
A simple model is good too for explaining attitude changes, manoeuvres etc (be sure to orientate it correctly so it shows things from the student's perspective). Ideally this is the same type of aircraft the student is learning in (high wing, low wing etc.). Also applies to using old instruments or engine parts when explaining functions.
A cockpit poster of the actually aircraft is also invaluable.
Try to keep it simple, but to the point, and always make sure the student is engaging in the brief by asking plenty of questions (eliminate yes or no answer type questions).
Be prepared to have a few different ways to explain a topic, sometimes people just don't get it. I found that by getting to know the student & their background it makes it easier to shape the delivery of your brief in a way that will work for them. They enjoy it a lot more and get more out of the flight when they understand what you're talking about!