I always store mine with the mag removed, safety on and the battery disconnected, in a gun bag, at work.
Magazine spring tension should be released by emptying mid or low caps or else you'll end up with mags that like to keep the last few BBs for themselves. I always released the tension on my hi caps too as if you leave them wound up in storage for a while they can get jammed (don't ask me how).
I always store my pistol with the mags empty of BBs but full of gas. The pistol is stored mag out, chamber empty, trigger pulled.
My shell ejecting shotgun is stored as per my real 12 bore : magazine and chamber empty, action open, safety on.
Always make them as safe and inert as possible, because the first thing people seem to do when they see a gun like object is to pick it up and pull the trigger (the mind boggles).
My real rifles are stored in one safe and the ammo and bolts in a different one, but I think that's probably a bit over the top for Airsoft kit ;p