I never pour paint from the bottle, nor do I shake the bottles for mixing. I use measured pipettes or glass droppers for transferring, I like the glass droppers because they can be cleaned thoroughly after use.
I use the metal Tamiya stirring paddle, to ensure all of the paint solids are scraped off the jar bottom. Then the little electric Badger mixer to completely blend all of the ingredients.
The paints can last for very long periods, when the bottle top rims and threads are kept perfectly clean, dried residue damages the ability for the bottle to maintain an effective seal against air.
The measured pipettes permit accurate amounts of paint/thinner ratios. It does take an extra few minutes to use these steps, but the paint consistency is rather important for me, I like having predictable results when laying on the finish.