If you know a tiny bit about the history of illustration, then you know that this guy is a power house: Joseph Christian Leyendecker. He is most famous for the 322 Saturday Evening Post Covers he painted and if you haven’t seen his work, please look him up.
I want to look at this study sheet of him because it is a superb example of how one can prepare for the final work.
If you have looked him up and compare his work to this study you will not recognize a big difference in the quality of his painting method. He did these studies as careful as the finished works.
Some parts are repeated over and over to find the best version for the final piece. For example the two versions of the hand holding the spoon. He did not change the position of the fingers, he changed the position of the camera / view point. Both hands are completely worked out. From these studies he can create the final painting with no need for models or photo reference. Everything he needs and more is there. He has enough variants to change his mind in the last minute.
I want to take these studies as a symbol for myself that should remind me to study even more, prepare better and to always give it my best shot.