then do marketing.
You can learn finance and accounting and media buying from a book. But the best way to truly learn how to do marketing is to market.
You don't have to quit your job and you don't need your boss's permission. There are plenty of ways to get started.
If you see a band you like coming to town, figure out how to promote them and sell some tickets (posters? google ads? PR?). Don't ask, just do it.
If you find a book you truly love, buy 30 and figure out how to sell them all (to strangers).
If you're 12, go door to door selling fresh fruit–and figure out what stories work and which don't.
Set up an online business. Get a candidate you believe in elected to the school board.
The best way to learn marketing is to do it.