Go to a library and borrow a basic colour theory book or something like an introduction to oil painting.
Doesn't matter if it's about painting flowers or landscapes, the principles remain largely the same.
You'll learn some of the basics such as for example Yellow Ochre can introduce an unwelcome undertone of greyness to a mix.
Similarly Titanium White can kill the vibrancy of a mix rather than adding a brightness.
To be honest the fun in using oils is experimentation rather than relying on a formula approach. Try out on an old figure or bit of plasticard to get a sense of the end result, one advantage of oils what you see in the wet mix is pretty much what you get when it dries.
If you're not too comfortable freestyling it just note %s and colours used below each mix on the plasticard and you have a permanent record.