Download Sony's ACID software. This music creation software is ideal for beatmixes and looping. They have a free version called ACID Xpress, but it limits you to only ten tracks. The ACID Music Studio has unlimited tracks, and that will give you freedom to use the full array of features you'll need.
Plan the mix. Most beatmixes are about an hour long. With this in mind, you need to have an idea of what the BPM (beats per minute) of the mix will be. Slower dance mixes are between 120 and 126. Mid tempo is around 127 to 133. Fast is 140 or higher. Set that in ACID Music.
Pick the music tracks. Pick songs that fit within the range of the speed of the mix. Load the track into ACID Music by double clicking on the song. If the BPM is unknown, it will open up the Beatmapper to determine this. Follow the prompts and click Next. At Step 2, it will calculate the BPM and display it at the bottom. Note the BPM in a file for future use or write it down.
Compile a list of samples and loops to use. This is what will make the mix stand out as an original piece, so take your time here. Experiment with each track to see what loops and samples mix well with it at the best places in the song.
In addition, you can create custom loops from the song itself. Load the song into a wave editor like Audacity (which is free) or Wavelab. Try to discover places in the song that can be a one- or two-bar loop. Us the editor's loop feature to make sure the loop is seamless; then import the loop into its own track in ACID.
Modify a track through the use of effects like delay and chorus. These come in ACID Music Studio. Other effects can be added as plugins. (Be aware that Acid XPress does not include the feature of adding effect plugins.)