Backup the software. If you're switching an existing laptop or desktop into an exclusive DJ computer, back up all important files onto an external hard drive. If possible, ghost or copy the whole hard drive. These files can then be available by simply using an available USB port and cable.
Format the hard drive. Starting with a blank slate will ensure that there's no conflicting software as well as free up space that can be used for storing high-quality music files.
Install the operating system. This is a straight-forward process. Follow the prompts that pop up during the installation. Make sure that the operating system is compatible with the DJ software that will be installed.
Upload music. Much of this may already be on the external hard drive and will be a simple matter of copying and pasting the files over to the internal hard drive.
Demo then purchase the software. There are more than a few companies now that have digital computer DJ software. Go to the manufacturers' websites and download the demos. The advantage of this is that you'll be able to evaluate how the computer works on a clean system as well as which software is the most intuitive. Some of the top software includes Native Instruments Traktor, Virtual DJ and PCDJ.
Test your output with a sound system. This may require an adapter to convert from a 1/4-inch to 1/8-inch connector. Connect to a sound system, check levels and play a full set. Sound quality is important and having an idea of what the mixes will sound like on a full PA system gives a better representation of what to expect in a live situation. It'll also save in set-up time as any glitches that may arise can be worked through ahead of time.