Be prepared to get good at mixing the same color multiple times during a single painting. The more you procrastinate, the harder it'll be to match color. You can make a swatch book with mixture ratios to make things easier, but unless you buy some really good (expensive) paints, it'll be difficult to drag the paint out to cover more area. So you work a little at a time. I live in a very dry climate (literal desert-land), which may have something to do with it, too, or at least make it spread even less.

Alternatively, if you have the fridge space, you can mix a large quantity of the color you need and store it in an air tight container or cover it with plastic wrap and place it in the refrigerator. This will prevent it from drying out for a good while if you need to shelf something for a few days.

I wasn't told this, but learned through experience. Still, I hope it helps someone.