In the second session with my oil painting class, I demonstrated premixing a palette that we'd be using for the flesh tones, the background and the hair. If you missed it, here's Part 1.
I'm a firm believer in premixing strings of color, it takes a little patience, but I think it pays off when you get into it.
I started with the background and worked forward, and in adjacent areas so that I could have good control of the edges.
I store my paint in a Masterson plastic palette with a cover. It's then wrapped in a trash bag and stored in the freezer. The paint will still be usable at our next class so all the mixing time and paint will not be wasted.
My understanding is that a home freezer doesn't get cold enough to actually freeze the paint but slows down the oxidation process which is what actually dries oil paint.
There is debate among artists about this but it makes sense to me. What everyone agrees with is never freeze your brushes or a painting! The cold will adversely affect your painting surface, the wood in the brushes, etc.
Be prepared to have your family complain about losing freezer space, a mini turf war of sorts. Especially when you have multiple palettes in there. (I'm up to three). The war generally fades to a rumble if you have your defense prepared. Go on long enough about saving time and money and you shall prevail!