It's amazing how many times people ask me, "Where do you get the ideas for your Speaking Tips?"
It rather strikes me as the same as my asking an accountant, "How do you know what to tell your client about his income tax?" Or a doctor, "How do you know what to tell your patient about his illness?" Whatever your profession, you've spent time and effort, not to mention money, to become knowledgeable and experienced. You've acquired a bank of information that you can draw on as needed to help your clients.