Highly dependent on ones specific financial situation, risk-tolerance, and employment trajectory.
While not a personal preference, most acquire revenue properties as they build equity over time. Assets secure lower loan rates, qualify mortgage fixed-payment schedules on investments, and require good management-companies to handle leases.
Generally, mitigating tax exposures by investing in small businesses is still popular. Sometimes they work, and sometimes they don't... but it is money people will lose anyway if they do nothing. Specifically, my first business investment was a few vending machine locations as a teenager, after a summer dropping hardwood floors.
Everyone starts somewhere, but blindly cloning what others do is usually unwise. ymmv =3
So basically, in order to have a steady stream of money coming in, you need to start with having a steady stream of money coming in? :-D
And often your investments will lose you money, so try to avoid the unprofitable ones, especially when starting out.
Indeed, most kids first big investment is in their schooling.
Sometimes folks have help, sometimes its all debt, and sometimes it pays off eventually.
However, living beyond ones means is almost always unwise. =3
Some spend their time investing from an early age... classifying assets and liabilities. My point was a few grand invested as a kid seems small, but will turn into a lot several decades later.
Others spend their lives making decisions out of impulsive narcissism. Unless you are a trust-fund kid, life can have very real consequences if things go sideways.
Most will learn the hard way... only lawyers and politicians get paid for excuses in life. =3