Make sure that your laptop is set up for audio output with a sound card and has a media player that will play digital music files like MP3s. Download iTunes or a comparable player such as WinAmp.
Plug your laptop into your mixer with RCA-to-mini (1/8 inch) cable and make sure that it is acting as a channel. Select Channel 1 on your mixer. Mixers have a range of inputs and outputs and support RCA cables.
Test your equipment by playing a music file. Make sure to have all levels including volume turned down as you test so that you don't blow speakers. Use a turntable or other laptop to plug into your mixer so that you have two active channels to play through your mixer.
Create a playlist of songs on your laptop. Purchase music from a leading online supplier like iTunes.
Organize the songs in the order that you want to play them. This will allow you to focus on cueing and mixing rather than choosing which song will be played next.
Plug your headphones into the headphone jack input or audio output on your laptop. Make sure that the output level is turned up.
Click on the first track or audio file in your list. You should hear the song playing in your headphones. You are pre-listening to the song that you will play so that it is the same speed or style as the song that you are currently playing.
Use the cue switch or knob on your mixer to listen to your input channels in your headphones. This will allow you to listen to either channel, whether it's a turntable, laptop or other input, or both channels at the same time.
Adjust the speed or BPM (beats per minute) of the song being cued so that it's to your liking. Most DJs keep a consistent beat range like that of house music, which is around 120 BPM, but some mash-up DJs mix in a range of styles and speeds.
Use the crossfader on your mixer to blend the pre-listened song with the one playing out loud. Slowly fade the out-loud track out by lowering the volume as you increase the volume of your pre-listened track.
Repeat the process for each song so that you have a consistent flow. Take your time when you are mixing with the crossfader so it's a smooth transition from one song to the next.