Lines of Communication
Either during the implementation of your bid for World Domination, or during your reign as Supreme Dictator for Life, the standard lines of communication will be severed. Communication is critical to your rule. You have to be able to have two way flows of information between you and your subordinates, and then out to the peasants. You need to make sure that back up forms exist.
During World War I and II, homing pigeons were used to send messages. It is true that pigeons often made a tasty meal for large birds of prey, and many messages did not make the final destination, but it is a form of communication that should not be ignored completely. In a pinch it will do. There has even been an implementation of IP over Pigeon. (Computers talking to computers.)
Do not use messengers. Men are too easily swayed. A good messenger is too hard to come by, and too easily dispatched by the enemy. Since man is always thinking of himself, your secret documents are more than likely sold to the highest bidder less than five minutes after they leave your hand.
Since transmission lines are easily severed, and because of the known difficulties of the above methods, you will be forced to rely on radio and microwave technologies. Although it is easy to block these signals, they cannot be blocked indefinitely. You can too easily bounce the signal around and get your message out.
Since radio communication will be pretty much required, you need to learn how to operate and repair radio equipment. There are many radio clubs with members more than happy to teach you this knowledge. Use them! Learn everything you can. These clubs are also a good source of future communication specialists for your future armies, or your massive propaganda machine.
Although many governments no longer require you to learn morse code in order to obtain a license to use radio, you are strongly encouraged to learn it. Since no one else is learning morse code, you would be able to tap out orders in the clear and no one would be able to interpret your orders.
Morse code could also be used in sending smoke signals. Granted, another faulty form of communication, but when in a pinch, you will use whatever you have available.
If you really need to get a message out fast and widespread, make use of the female gossip channels. People twelve hours away will hear you message less than ten minutes after you have finished giving the message. This is still a mysterious phenomenon, but it exists, and as Evil Overlord, you are not above using whatever is at your disposal.
The point is, always maintain lines of communication. If one line goes down, follow a set method of transferring to another form. Always have a back up. As soon as you can, get the previous method back up in working order. A successful Overlord is a well informed Overlord.