A DJ's primary goal is to entertain his audience, to seamlessly adjust the atmosphere and rhythm of the party so all can have a good time. If he is not in touch with what kind of crowd he is dealing with, his efforts can lead to unhappy party goers or radio listeners who will change the channel. To be a good DJ, you must pay attention to who makes up the crowd.
Know music--not just the music that you personally like but what works at a bat mitzvah or trendy club. Keeping current on hits in different genres will ensure you can deliver crowd favorites. If you are good enough to specialize in one type of club it is even more important to stay current or even ahead of the music scene, putting you in a position to pick out hits.
The very basic equipment needed is a music library on any preferred medium (CD, vinyl, MP3, etc.), a DJ mixer that allows different songs to fade in and out, something to play the music, headphones, microphone and of course an audio system to broadcast sound. Many DJs also utilize more specialized items such as samplers and digital effects machines. These allow them to blend and add sound in a more complicated manner than a simple playback.
DJing can be a hobby or a career. Many people have some basic equipment and work the parties of their friends and relatives. In the hopes of landing a consistent paying job at a radio station or nightclub though, some aspiring DJs hold promotions, parties, where they can showcase their talents. When the party goers have a good time they will spread the word, helping to build the name of the DJ.
People began spinning records early in the 20th century. The first was Ray Newby in 1909, playing records on a small spark transmitter. In the 40s the first dance parties with DJs playing records were held. The 60s and 70s saw a growth in preference for live music and a decline in the use of DJs. However in the 1980s, with the advent of the synthesizer, DJing really came into its own as the DJs could now add a personal touch to the music as opposed to just deciding the order of play.