I have 2 pioneer cdj 800’s and a djm 500. I downloaded audacity a few months ago and I still cant figure out how to record my live dj sets properly. I have my mixer connected into my laptop using a RCA cable. When I try to record my set audacity records from my computers mic instead of the mixer goin into the laptop. So when I play back the recording you can hear any noises you made while recording, for example if I coughed it would be recorded. I have pluged my mixer into the mic and headphones input and nither seem to record from the mixer properly!! If anyone can help in any way I would really appreciate it because its driving me mad!! 
You probably have the built-in mic selected as the recording device in Preferences → Devices → Recording. You need to record from line-in.
Most laptops don’t have a line-in though and you can’t connect a line level signal to a mic input. You probably need an external device such as this: http://kozco.com/tech/audacity/pix/UCA202.jpg
The device in the picture is a Behringer UCA-202.
I thought I would have to get a device like that but wasnt sure on what type I would need. Ill go get myself one of those 
Thanks for your help