I don't use this technique for every oil painting, but if you're feeling lost on what hues to use, sampling from a master work can help guide your color choices.
In 2010, when I was working on Beautiful Grim, my inspiration was John Singer Sargent's Lady Agnew of Lochnaw. I was privileged to see it at the National Gallery of Art in DC about a decade ago, and it's been one of my favorites by J.S.S. since. So while I let Lady Agnew set the mood for my piece, I also let it direct some of my color choices, particularly the skin tones.
No digital reproduction will ever be accurate to an original, but I was able to use colors sampled from Lady Agnew to create a skin palette that had a similar value range and close hues. By printing out the sampled colors on a card using a calibrated photo printer and photo paper, I'm able to easily mix paints next to the cards: