1. Save enough money so that you can live off your investments in a minimal way while working on your project. How od you do this? Calculate your yearly spend and multiple it by 25. Need 100k per year to survive? That means you need 2.5 million invested in index funds in order to "retire" and be able to withdraw 100k/yr from your portfolio to use.
2. Save enough money to cover your expenses for a set amount of time. Think you need a year to prove that your tech works? Save up enough money to cover your living expenses for a year.
3. Raise funding. If you can convince a VC that your idea has a probably chance of success, there are VCs willing to take risks on it. Getting VC funding will allow you to pay yourself a very small amount of money to hold you over while you build and experiment with your tech.
4. Survive with the help from a family member/spouse. Move in with your parents for free rent/food, or live off your spouse's income for a while as you experiment.
These are the primary options most of us have.
1. Save beforehand: Save six months of living expenses. Estimate cost of technology validation, and multiply that by three
2. There's no same in working part-time as a barrista or waiter/waitress.