1. Know that information sells.
You can not sell a car in the newspaper with an add that reads "car, four wheels, goes places" The same applies to selling your wow account. "WTS 120 Mage 100000 gold" is not a good enough title.
2. Begin with the body of your ad.
Here, you can be more descriptive and should mention character progression, what gear you have, etc. - It is important to remember that a picture is worth a thousand words. You can describe a sports car to someone that has never seen one.. they won't go "Ooh!" until they see a picture. The easiest way to take a picture of your warcraft, wow account is to get a character profile using a hidden armory. Do not make overstatements about your account, you buyers will lose trust the same way that you trust someone that knocks on your door and says they have the best vacuum cleaner in the entire world.
3. Many buyers are not experts.
They can't translate abbreviations or value items that are only named and not shown. (Explain that your Scarab Lord achievement is owned by only a handful of people in the world and send them an article about it)
4. Prep your account.
Deguild, wipe friends list. Stop recurring billing of your credit card. You might even want to tell a few friends so that they don't freak out and email the game company that some stranger is playing your account and you were obviously hacked.
5. Show your price in the title or body.
This is important for forum selling. Some shoppers get discouraged if they have to ask and they simply will not ask nor make an offer. Consider your last trip to the grocery store, if you wanted something and the price wasn't right there, you might have just skipped buying that item. Convenience is key!
6. Get all the account information ready.
That includes account name, email, password, secret answer, CD keys and a picture of your ID. Also make sure to remove your authenticator and SMS protection.
7. Be prepared to accept PayPal.
If you don't have a PayPal account, get one. If you don't know how to use PayPal, learn.
8. If your account is inactive, activate it so you can prepare screenshots if needed.
9. Don't ask potential buyers, "Are you going to steal my account." - If they are a thief, they might be a liar. Think about it.
10. If you have alts that are high level or have rare items/achievements, you can sell them separately.