One thing that I've been doing a lot lately is a lot of critical listening. And in doing so, I'm finding out that what really makes a mix sound big is the contrast between your background sounds and those up front and in your face, your mono sounds and those that are stereo, and so on. It's being able to make everything fit by way of compression, eq, and effects. Also, if used efficiently, these three can make your sound field appear much larger than it started before it was separated and mixed. It's just getting the perfect combination between ALL three is the tough part. Level the mix, use eq and compression to make everything melt together as a whole and to let everything be heard. Then go to effects. At this point you should at least have an idea of how you want things placed within your mix. Some things will work out to what you imagined and others things will need to be improvised. Improvisation can be one of the biggest keys to mixing.
Now this is what I'm LEARNING....I'm damn near in the same boat with you
but I'm getting close.