Keep playing Mega Moolah. This is an oversimplification, but it holds true. The jackpot is claimed in a randomly triggered bonus round, where even a 25c bet has a chance of getting the highest payout. Microgaming don’t disclose the actual percentages, but they claim that higher bets have higher chances of winning the Mega Moolah progressive, even though even the smallest bet can do so, too. But, of course, there is no actual rule here, someone might play on the highest bet for ages and not win a progressive, whereas someone could grab it even with a single spin of 25c.