How to mix in 3D: width, depth and height

Treat your mix as a 3D space instead of a flat line. Left and right come from panning. Front and back come from volume and reverb: louder and drier sounds are closer, quieter and wetter sounds are further away. Up and down come from brightness: bright sounds float, dark sounds sink.

How to do it

1. Decide what's in front: usually the vocal, kick, snare and bass. Keep them centred, loud and fairly dry.
2. Pan supporting parts (hats, percussion, guitars, keys) left and right.
3. Push background parts back with lower volume and more reverb.
4. Use EQ for height: brighten what should float on top, darken pads and fillers so they sit lower.
5. Check on headphones and speakers. Every part should have its own spot.

Why it works

When everything is loud, centred, dry and bright, the sounds stack on top of each other. Giving each one a position in all three directions lets you hear every part at once.