Winning listeners over is easier if you know the four things people find most interesting: sex, health, money, and themselves. This is somewhat of a cynic's list, but most good speeches will tap into one of the things, usually the last item.
Because people do things for their own reasons, you must motivate and inspire people from their perspectives, not yours. If you speak to their real needs, they will be compelled to listen, and listen well. In my own seminars and speeches, I always find out one or two specific problems that the audience currently faces. Then I construct a speech that solves—or shows people how to solve—those problems. This is the speaker as hero or heroine, the problem-solver approach, and I recommend it highly. If you're speaking to middle managers on running their departments more efficiently, and you determine that one of their problems is motivating clerical employees, then give them a strategy to do just that, with results that tie in to what the corporation expects of them.
Whether your audience is one person or one thousand, you should focus on its needs. Being successful in one-on-one situations requires you to focus on the other person. Start any general communication by putting yourself in that other person's shoes and proceed from there.
Addressing problems your audience faces illustrates the importance of context. So does this story: Suppose you came to a seminar and, instead of the promised speaker, you were met by a desert survival expert. You probably would not listen too closely. But if the pilot of a plane being forced to land in the desert gave that lecture, you would view that formerly irrelevant information quite differently. Context is caring—what does your audience care about? Figure that out, and you're well on your way.