Turn on your Apple computer. Locate and click on "GarageBand's" guitar icon in the dock menu along the bottom of your screen.
Open your recorded "GarageBand" project. Click on the "Recent Projects" button on the welcome screen. Select your recorded project and click on the "Choose" button to open the project.
Notice the specific tracks in the editing window. This can include a series of guitar, bass, keyboard, drum and vocal tracks. Determine the elements of the song you want to highlight. This largely depends on personal preference or the style of the song. For instance, a folk/pop song will feature a strong vocal part, so the instrumentation should be balanced in a way that highlights the strong vocals.
Adjust the volume of each track until each track has a balanced audio level. Each track located in the window's left side panel has a virtual volume knob that you can adjust with the mouse's cursor. Turn up the lead vocal track to the desired volume level. Then slowly bring up each instrument one by one. Start by bringing the guitar, piano or main accompanying instrument up in the mix. Then bring up each instrument individually by adjusting the volume knob.
Use the panning feature to improve the stereo quality of your mix. This is another virtual knob on each "GarageBand" track that allows you to shift each audio track to the right or left speaker channel. Stereo panning is a hotly debated aspect of mixing, but as a general rule, avoid hard-panning -- that is panning any one track all the way to the left or all the way to the right.
Add effects, like reverb, delay and distortion to give character and enhance each track. Click on the track you want to add effects to and click on the "Edit" tab on the right side panel of the window. Click on an empty effects box and select an effect from the drop-down menu. Then click on the effects icon inside the box to adjust that individual effect's settings.