Chapter five of Paul Anderson's Technical Writing text details methods for persuasive writing. Persuasive writing is either meant to influence attitudes and actions, or to encourage more effective collaboration, and works to reverse an attitude, reinforce and attitude, or shape an attitude on a subject on which your readers currently have none.
The first point the book makes about how to be more persuasive I believe is most essential. It states, “to communicate persuasively, you must listen well.” Listening and being flexible allows you to shape your communication for greater impact, and even revise your thinking to determine a more effective idea than your original idea.
Focusing on a reader's goals and values is the next most important aspect of persuasion. Know their organization goals and values, their personal values, and their personal goals.
Anticipating counterpoints can temper your thinking and help you design a more persuasive communication. Acknowledging counterarguments preemptively and then providing reassurances against them can demonstrate to the reader that you understand and have considered their concerns.
Providing sound reasoning and solid supporting evidence is very useful in persuading a reader. This employed with proper organization, can present ideas to the reader in an order in which they may be more receptive to the data they are given, and thus to your recommendations.
Building a good relationship with your readers will also enhance their receptiveness to your message. Establishing credibility will help them take you more seriously, and presenting yourself as an ally will prompt a more sympathetic response to you. Additionally, understanding when and how to appeal to a reader's emotions can affect your persuasiveness. Not all writing should appeal to emotion, but it can be a powerful tool if employed properly.
The chapter again covers largely intuitive concepts. Understanding your reader will make you far more persuasive.