I'd say this is terrible advice for a beginner. You can ruin a coin much more easily than improve it.
French is of the old school of numismatics that believe cleaning was okay. Reading any of his books you will see he has always been on the side of cleaning. I have a beginners book of his from 1989 where he devoted a chapter to cleaning coins.
Would you like some nice shiny Lincoln cents or any other copper based coin? Take some low value coins and place in a vinegar salt solution. Bingo! Instant brilliance. Don't forget to wash.