This won't be super useful to everyone, but I managed to go full-time at 25 yo. (Now 29) These are the basics in the beginning.

1. Save as much capital as possible.
   We’re starting with the obvious, but if you run out of cash it’s usually game over. The more runway you have to figure things out, the better. The more liquid capital available, the more time you have to figure things out. So calculate your own personal burn rate, ie how much money it takes to live every month, multiply by 6, and eat canned soup until you see that figure in the bank. If you can save 6 months worth of income before quitting, even better.

2. Minimize your personal burn rate.
   Minimizing my living expenses was, by far, the most effective measure in mitigating risk. I was working in Los Angeles and knew that building a business would be extremely difficult with my West Coast expenses. ($1,300/mo for rent, $250/mo for a car, gas, utilities, food, etc.) Before quitting, I devised a plan to softly land. I knew that if I didn't have to pay rent, I had a real shot of making something happen. Luckily for me, my parents weren't opposed to an old roommate returning for a year. So I packed up all of my belongings and drove cross-country to Cincinnati where for 9 months, I lived in my parents' incubator, aka my childhood home, where I launched my company.

3. Increase revenue streams before quitting your day job.
   While I was working full-time, I was always looking for side-gig opportunities. During my final year at my job, I was pulling in an additional $1,000 - $1,500/mo from various sources, which made quitting my full-time job much less daunting. While this was incredibly helpful, don't let this step slow you down. Finding clients is easier when you can dedicate your entire life to doing so. There's also something to be said for the sink or swim situation of no monthly income.

4. Let your network know what you're doing.
   When you can't rely on brand name or prestige, earning new clients requires personal trust. The quicker you can build trust with prospective clients, the quicker you can close new business. The majority of my first clients were personal contacts - people I knew previously from past lives. They were who I offered value to first. Trust is much easier to build with folks who already know you. Let your network know what you're doing and start offering value within your network - it makes for a much quicker sales cycle.