Djing basic technics include: Music selection, blend timing, music key matching, and beat mixing.

Music Selection

Selecting music is all about picking the correct jam while djing.  If you are djing on the radio your music selection can be a little different than when you are spinning at a high school, college, or club party.

First, learn all the popular jams of the audience that you will be playing to.  The hardest group to cater to in my opinion is the college party group/club group.  This is because you have people who already know what they like. 

The best experience in selecting your music is by mimicking from someone else. This means that you should go to college parties to listen and analyze what the dj is spinning, and the reaction he gets from his music selection. Take a pen and pad.  When you hear a song that the dancers seem to reaction well to, find out the name of the song and write it down. This is a form of keeping your ear to the street. You can also do the same music research by having a good relationship with the music shop you frequent.

Blend Timing

Blend timing is knowing the right place to change a song.  This skill normally is developed when you practice in your home studio. Usually you blend in or change to the next song when the high point of the song or the break has completed. This is done with the intention of keeping the party mix hyped. Most if not all songs have a high point or climax somewhere in the middle of the song.  It's the part that everyone remembers or the point that everyone enjoys the most. It becomes very easy to recognize after a while.

Musical Key Matching

Being a deejay requires musical understanding.  Just like playing a piano or saxophone you need to recognize the different musical parameters of a song. The the sake of simplicity we will divide the the musical keys into two distinct parts, major and minor.  A song that's in a major key will sound happy or energetic. A song in a minor key will sound scary or ominous.

As a rule you will mix major key records with major key records, and minor key records with minor key records.  This is the rule.  The exception is if the sound playing goes into a drum break. Meaning that only the drums are playing without and note playing instruments playing. When you have a drum break you can mix anything you what as long as it's on beat.

Beat Mixing

This is the defining skill that shows a dj's actual chops. If you can scratch like Qbert, but your beat mixing is weak, then your worth as a dj is diminished.  It's far better to be able to blend songs well than to be able to cut like Jazzy Jeff. It would be like being able to slam a basketball like Jordan but not being able to dibble or pass. Your dunk would be great, but you would have no game.

Beat mixing is the main thing. A good way to practice your beat mixing is to take two identical songs and mix them from beginning to end. When you do this be sure to notice the music aliasing. Take control of the phasing between the identical songs on each turntable. Practice eliminating the phase. This will give you the ability to mix two different song on a perfect beat.