What can I do in my 20s to become a millionaire by 30?

Invest. It would most likely be a high risk investment as the lower risks ones do not give you the required amount to hit the 6 figures savings. A high monthly salary and passive income will help as well. All the best!

Within a decade to be a millionaire:- the most important is your income.

You can save 90% of your salary, but if your salary is only $50,000 per year, that makes it less than $500,000.

If you save only 20% of your salary but you earn $500,000 a year, thats goes to a good millionaire status.

Of course most of us would be somewhere in between, and we build up our salary with investment in stocks, ETF, etc etc.

To build it up, build your pay.

to build your pay, build your skills.

If you prefer to be employed, go for courses go for skills that the market demands currently.

If you prefer a higher pay, go for business. Start small start young. Most businessmen don't get rich investing in ETF or investing in stocks, they get rich investing in their own businesses with a much better ROI.

Dream big!

There are only a few possible ways where you can hit a million by 30:
1) You have a high starting pay of >10k a month and save and invest a lot
2) You are in a sales job and are super good at it (e.g. Some financial advisors)
3) Starting with a high capital base (>100k) and investing aggressively - this may be a stretch
4) Start a successful business
5) Strike toto (do not bet on this)

All in all while having a million by 30 is a nice goal to have few people manage to achieve it! You can do a spreadsheet to see what is the amount of savings and return that you need to achieve it.

Great dream you have out there! Not impossible, but the road there might seem impossible. A few things off the top of my mind is to minimize your expenses, only spend what you need and not want, fully utilize all credit card & bank accounts as you can.

These 2 above actually still doesn't bring you close, and I think you would have to take more risks to reach there, and for me that's investing my $ in huge growth potential companies. And the most riskiest way would of course be to start your own business, being an entreprenuer. But it would take a lot of courage and emotions (and luck) to make it out as well!