I'll side with PJ and Stik on this, clean bottle/cap threads are your first best practices for effective paint storage. I've read several times, that any additive to paint in an attempt to prolong storage life is of no benefit, and actually can contribute to the paint going bad in the bottle. Can't explain why, maybe a chemist type will drop in with an opinion.
Speaking only for myself, I have many OLD bottles, even a few Pactra, and it's been off the scene for years. Regardless of the brand/type, I never shake the bottle at any time. I first stir it well to get all of the solids off the bottom, then I use the Badger stirring mixer for complete blending of everything in the jar.
I use pipettes or even straws with a finger over the end, to transfer the paint from the bottle to the small cups I use for blending thinners and flow aids, if used. That way the bottle and cap threads stay perfectly clean, and will allow storage for very long times. And a firm tightening of the cap is important, to keep air from evaporating the ingredients that make up the paint.
My Tamiya, Testors, Humbrol and other paints can be dependably stored for very long periods, by just following those practices.
Patrick