One thing life has taught me: if you are interested, you never have to look for new interests. They come to you. When you are genuinely interested in one thing, it will always lead to something else.
If a speech is to be of any importance at all, the speaker should live with the theme or message, turning it over and over in his mind. He will be surprised at how many useful illustrations or ways of putting his case will come to him as he walks the street, or reads a newspaper, or gets ready for bed, or wakes up in the morning. Mediocre speaking very often is merely the inevitable and the appropriate reflection of mediocre thinking, and the consequence of imperfect acquaintance with the subject at hand.