Whats the proper way to plug a laptop into mixer into a pa system? We are playing prerecorded guitar parts if that matters. thanks!
There are many ways to accomplish that and it really depends on the mixer and what interface (if you have one) you are using. Generally I just either use the CD in on my Mackie when playing from an iPod/iPhone (don't use the earphone jack, but the convertor adaptor that plugs in the botton) or if I have the full iMac (or any computer) it goes through the M-Audio Fastrack Pro outputs into a stereo (two channel) fader on my mixer. Try to avoid using headphone or earphone jacks into mixers, it is not a line out and can sound like crap.

The big trick is how do you synchronize everything to your recorded track and control it.