First of all, make sure that the Homeplug is connected directly to an electrical socket and not to a trailing socket, extension cable or extension reel. The reason for this is to prevent interference. Using a Socket Homeplug that includes a built-in socket point will mean that you won't need to do without one of your electrical sockets. Your existing socket will still be available (see image below).

 
Another useful tip is to connect your Homeplugs to the same group within your electrical system, especially if you are installing them for the first time. You can do this by setting them up in the same room, for example. Once a link has been established between the Homeplugs, you can then increase the distance between them, by inserting them into electricity sockets elsewhere in your home. Once they have completed their initial installation, the Homeplugs will be able to reconnect to one another quickly and easily. 

If the electrical system in your home is made up of a number of phases (which is only rarely the case), you must make sure that your Homeplugs are connected to the same phase. Otherwise, they will not be able to connect with each other.