Look into microphone polar patterns. Mic placement is critical (Monk at the Five Spot) puts you in the club (took them two nights to get it right) A good engineer can picture the mix before entering the studio. Width and depth are often discussed - height is often overlooked. Never forget we are listening to the room first - then the speakers. Learn to identify reverb decay times. Roger Waters "Amused to Death" (not the remaster) is a good learning tool. Jethro Tull "Masters" CD contains a few good mixes. Never forget - a phase coherent mono recording played back on two speakers becomes stereo because of room reflections.