He better watch sports matches first. That will be a gambler's introduction to the game. Next, he should not be betting high stakes just yet. Test the waters. There's so many games to bet for and it doesn't need to be rushed. Just play some minimum amount and check if you are doing it right.
A gambler should not gamble first without even knowing what he is getting into. Watch the sports, learn it, and then maybe a gambler has the talent to predict the right choice.