It's quite simple to dilute paints. At a ratio of 2:1, you would take, for example; 2oz of paint to 1oz of thinner (or whatever you wish to use as a paint thinner). You can sometimes eyeball the ratio, but if your doing a custom color use a dropper or a measuring cup (or jar).
Or vice versa to use as a lighter coat.
There really is no specific dilution formula, it's more of a preference that will set your standard for applying paints.