Foreground/Background
The basic element of mixing is the loudness of each track. This is the first place you should start as a budding engineer. No matter what system you own, from the 4-track to Pro Tools, volume manipulation is available to you. In visual artworks, such as paintings and photographs, there are background and foreground; the more important visual elements usually come to the front of the work. It's the same with audio — the important parts need to be heard.
The mute and solo buttons are the two most important buttons to use in mixing. Get to know and love those buttons. When you mix, you'll never be able to work on a full mix all at once — it's just too much sound at once. Isolating sounds or groups of sounds played together is the best way to go, especially when working with EQ problems. Focus on small parts and build your mix around them.
The volume control on a mixing board or your software recording device is called a “fader” because it allows you to fade the sound in or out at will. The first thing you should do is set your faders for each track to create a basic feeling of foreground and background. In most music that includes vocals, the vocal track is usually the point of interest and should be the loudest thing you hear. But how loud? How much louder than the accompanying guitar? You have to trust your ears on this. At a basic stage like this, do your best to get it to sound as balanced as possible. Volume of the tracks is only one very basic element of a mix. But it's a great place to start!
