Prepare your set list in advance. If you've been booked to DJ at an event, consult with the client and make a list of song requests she may have. Find out the average age of the attendees, and let this inform your song choice. For example, if it is a "Sweet Sixteen" party, include some current pop songs. If it is a 50th birthday party, select some songs from the 1960s that the birthday boy or girl would have grown up with. You don't need to include every song in exact order, but make a note of songs that you definitely want to play at certain points. For example, "For He's a Jolly Good Fellow" after the speeches.
Execute smooth cross-fades. Cross-fading is the process where you mix the end of one song into the introduction of the next. Cue up the next song in your headphones approximately five seconds before the end of the current one. If the left turntable is currently playing, move the headphone slider dial to the right so you can hear the next song on the right turntable. Gradually move the master fader from left to right as the song comes to an end. The master fader is typically located in-between the two turntables.
Match the beats discreetly. In cases where you need to fade a slow song into a fast song or vice versa, beat matching is the most seamless means of doing so without disrupting the flow of music. Cue up the next song in your phones and count along with the beats. Remove the phones so you can hear what is currently playing, but keep counting. This determines which song has the faster tempo. If the next song has a faster tempo, gently touch the turntable of the cued song to slow it down to the same beat as the next song while moving the master fader over. If the next song is slower, do the same but touch the turntable of the song currently playing.
Monitor the mood of the room. If people are dancing and enjoying themselves, stick with the style of music you are currently playing. If you put on a record that "clears the dance floor," let it finish and revert back to the style that had everyone dancing. Don't be predictable, but don't radically change styles if your customers are having fun.