In the first two images I show how you can use a thin layer of hot glue to insulate a breadboard. This is useful if you are making a metal enclosure or if you are worried that the breadboard may come into contact with other components in the enclosure. As shown in the third image, electrical tape is also a good choice for these situations (although sometime sharp points in the solder may poke through the tape).
In last two images you can see how I used hot glue to support and insulate the leads on an audio jack. This way there is no chance of a short circuit and the soldering joints are less likely to break.