So you have a lesson that you want to teach your audience. Good for you! But before you do you might want to read this here page.
Necessary TropesWell, obviously there's going to be an Aesop. After that, it depends on the Aesop you're using. Many good morals can be derived from a properly Deconstructed Trope, from the obvious "Don't believe what you see on television", to more specific items, such as "No, you can't change him."
Choices, ChoicesThe world is your oyster when it comes to Aesops but just in case you're not sure what you want to teach your audience check out our handy-dandy list of Stock Aesops.
Potential SubversionsPick an Aesop, any Aesop, and subvert it. Space Whale Aesops are really good for this.
Suggested Themes and AesopsAgain, the world is your oyster, but make sure that whatever Aesop you pick doesn't get cancelled-out by your premise. Also, make sure that your series can deliver an Aesop that your intended audience can handle reasonably well.
Set Designer / Location ScoutHaving your Very Special Episode take place in its original setting will drive your Aesop closer to home than if you change settings all of a sudden.
Props DepartmentMake sure to have Aesop-related props nearby (car and booze for the drunk-driving episode etc.).
Casting DirectorIt might be tempting to bring in a Long-Lost Uncle Aesop but it might be more meaningful if you either introduce them several episodes prior or if you use an already existing character (for example, if the drunk driving episode is one where Tonight Someone Dies).
The GreatsGargoyles had one about guns ("Deadly Force", currently a Missing Episode), and about reading ("A Lighthouse in the Sea of Time").
The Epic FailsCaptain Planet and the Planeteers had a few.