Congrats!
How have you done it - stocks, real estate, starting a business, other?
The most fundamental way possible:
Spending a heck of a lot less than what I earn.....since long before discovering Jacob / ERE and subsequently MMM. (Shout out to Jacob for crystallizing / providing a framework around which my habits / inclinations could gel.) Time is your friend, although I wish my natural inclinations had been toward a 40-60% savings rate when I was younger, in lieu of 20-ish percent. I'd be FI by now.
After that, its all flavor......yeah, stocks, bonds, RE that could be an asset that (in my book) currently isn't (as in, I live in said RE, so there's no net cash inflow, however it does provide the non-cash utility value of shelter, and I suppose I could rent it out and move it to the "asset" side of the ledger at whim, in which case I'd be at 28-30x expenses). I'd though about a business in the past, but didn't do it do to changing circumstances.
So nothing magical - modest savings rate when younger, coupled with a much higher savings rate in recent years.
Future: I'll look into rental RE for part of getting from 20x to 33x and beyond, if it pencils out in my local market.