Facts are funny and complicated things. Facts, when used well, enhance the credibility and persuasive force of an argument. However, facts require context and argumentative support to be used most effectively. Using clear and well-researched facts tactically to support your argument, you will signal to your reader that real-world data has been collected to support your point. Be careful, though, a big list of facts without context or argument is often confusing and counter-productive.
Think of a persuasive or argumentative essay as a journey. You want to lead your readers along a carefully chosen path to a destination upon which you have decided. Your arguments and evidence are the stepping stones to this destination. Different sources suggest different order to your arguments -- strongest argument first or last, for instance -- but each essay will vary. In general, avoid lumping a series of weaker or stronger arguments together. When you do this, you risk making your paper seem disjointed. Make sure your arguments flow logically from one another, and that weak and strong arguments are linked together, giving the paper a coherent structure.
Ultimately, a persuasive or argumentative essay aims at convincing readers of something. This requires a thesis or theses. No matter how strong your arguments and evidence are, if the reader cannot remember or understand your thesis, then you are in trouble. Clearly state your thesis in the introduction and conclusion of the paper. Also, throughout the paper, especially if it is long, remind readers of how a particular fact or argument relates back to the central thesis of the paper. This keeps the reader's attention and makes your arguments seem more coherent.
Writing well and clearly is an important part of any writing assignment, but it is particularly important when writing an argumentative or persuasive essay. Even if your thesis, facts, and arguments are sound and strong, poor or unclear wording, sloppy grammar, and bad spelling distract the reader and zap her confidence in the piece. Persuasion requires not only solid evidence, it also requires good style, structure, and coherence. Editing your paper will help achieve this. Read your paper aloud to catch awkward wording and have a friend or colleague look at it before submitting a final draft.