#1. Show how the other person benefits from listening to you
Sun Tzu, in his classic The Art of War, said that a person who knows both the enemy and himself need not fear the result of a hundred battles. Apply this principle when persuading other people. They care more about the benefits to themselves than to you.
#2. Have answers to objections
Even if people agree with the benefits you've outlined, they might raise objections to your idea. How are you going to react? If you've thought about the Sun Tzu teaching of point 1, you may have already anticipated those objections and can resolve them. The more you anticipate and prepare to answer objections, the greater your chances of persuasion.
A user might not want to call the help desk because he knows Joe in IT can answer his question quickly. To address this objection, you might ask what would happen if Joe were sick, on vacation, or otherwise unavailable.
What if you can't answer the objection? Be honest about it. At the same time, however, you still might be able to persuade the user that other benefits outweigh his or her objection.