Choose a theme for your top five reasons. While top five articles do show five different things, they should not exist in a vacuum. Rather, each item should attack the same theme from a different angle.
Jot your top five reasons down based on the theme you chose. Better yet, jot down seven to 10 reasons. This will give you more room to work -- if you have seven good reasons, you can then choose the five best reasons out of those. However, it is important to write your reasons down before you write any content to avoid repetition.
Write an introduction that explains the basic theme of your top five reasons. If you're writing "Top 5 Reasons You Should Visit My Hometown," and your hometown is known for its friendly local culture, then explain this theme in your introduction.
Write a paragraph or two on each reason. Remember that good writing needs to be concise.
Write a conclusion that sums up your article's theme. This isn't absolutely necessary, as the fifth reason can serve as a conclusion.
Go back over your copy and make sure it reads well. You will likely find a number of places that need changes -- do not hesitate to make them. Good writing comes from good editing; very few people produce high quality copy without at least a second look.
Submit your article.