For a time, Steinbeck lived and worked with migrant workers from Oklahoma and California. The result was "The Grapes of Wrath" and a Pulitzer Prize. These words of wisdom are from a letter he published in 1963.
Steinbeck's best advice to a writer is, "If there is a magic in story writing, and I am convinced that there is, no one has ever been able to reduce it to a recipe that can be passed from one person to another. The formula seems to lie solely in the aching urge of the writer to convey something he feels important to the reader. If the writer has that urge, he may sometimes, but by no means always, find a way to do it. You must perceive the excellence that makes a good story good or the errors that make a bad story. For a bad story is only an ineffective story."
Steinbeck's advice echoes the advice of many other writers: write what you know, something you feel is important that only you can tell.
Steinbeck was awarded the Nobel Prize for Literature in 1962 and died of congestive heart failure at the age of 66.