Another way to look at this type of essay is to see it as a challenge. You, the writer, present a response to someone, the audience/reader, who has disagreed with you on a specific point.
For instance, if you want to write your essay on whether or not shoes should be worn inside the home, you would choose a side and prove your point. Either you are proving that shoes should not be worn indoors (and proving this point to someone who disagrees) or you are proving that shoes should always be worn in the home (and proving this point to someone who disagrees).
As stated in point 4, proof is the most essential element in this type of essay. State your point up front. Then prove it.
When writing a persuasive essay, it's important to incorporate the various elements of persuasion. You should be passionate about your topic and use your voice to convince readers to be on your side of the issue. Even if you are writing about something that you aren't passionate about (because it's for a class assignment) pretend you are and really put it into your voice. You should also try to appeal to your readers' emotions. If you are arguing about something controversial, tell an anectdote, putting an image in the readers' minds.
Make sure you have logical reasons to support your argument. Saying that someone should do or believe something because "it just makes sense" or "because everyone else believes it" is not valid and logical. You need to back up what you are saying with valid information and facts. On that note- use resources and definitely do not make up information.
Another thing to be aware of is that you do not want to threaten or bully your reader, and you don't want to let your own emotions get involved. Let common sense, logic, and your research to the persuading.
Litteacher has provided a great explanation regarding this type of paper. One thing that I would suggest is offering the opposite side of your argument (if you are for dress codes in school, offer a good reason why dress codes would be bad). By offering the alternative, you are showing your reader that you have examined the concept fully and have taken an educated stand.
Basically, you need to state a position and defend it to the point that someone else will take your position. The key is to choose one strong position, and not be on the fence between two. Then, you want to be as specific as possible in defending your position with facts and arguments. I think the best way to start the essay is with some kind of emotional statement related to your topic, to emotionally engage the reader.