Width is about how much left and right an instrument is panned (or in the middle). Sounds easy but the possibilities are countless.
Panning a sound left and a very short delay (lets say under 15 ms) panned to the right, gives the impression of wide sounds. Read something about the haas effect:
http://edmproduction.wikia.com/wiki/Haas_EffectListen with headphones:
https://www.youtube.com/watch?v=-PFgCrvwByoChorus, phasers, flangers and delays are all tools that give you a chance to play with stereospreading.
A stereo reverb on a mono sound can give a nice stereospread too, although the source stays mono.
About depth; volume faders are your friends; volume lower is futher away in space, louder is more in your face.
Reverb plays a big part in perception; more reverb, it will sound further away.
Make use of the proximity effect:
https://en.wikipedia.org/wiki/Proximity_effect_(audio)
When you roll off lower and higher frequencies, you create the effect that something is further away, add those frequencies and it feels like something is closer to you.
Here's another video about depth:
https://www.youtube.com/watch?v=7MdE1adTCu0&list=RD-PFgCrvwByo&index=5When you automate all these effects, you can create movement through space.