A good place to start for big sounding mixes is Phil Spector. But he wouldn’t know about pan law as he always worked in mono.
I guess all the advice given points to “if your mix still sounds big in mono it is actually that big.” VERY fine attention to detail of voice balancing and the least amount of compression you can get away with while still recording a strong fundamental signal from the instrument in the first place.
Basically, and I’ll probably be proved wrong, if you record a mouse squeaking you’ll have a lot on your plate making it sound like a lion. There are many ways of making it sound like a big mouse though.
Pan your strongest voices (usually the mid range; boning up on orchestral instrument typical pitching, if you work with “normal” instruments would be a good idea) in the material towards the centre, and the listener, and group all other weaker material out of it’s way, either more centred or more out to the edges. I wouldn’t worry too much about pan law unless, like the other contributors here, you are aiming for a specific purpose like broadcast, games or movies where the listener might have less than optimum speakers but that signal needs to get thru without artifacts or distortions being introduced at their end.
And first always ask yourself what you would do if you wanted something to sound small. Then do the opposite. 
And this: