My experience from having left a job as Project Engineer, to launching my own company. And having mentored dozens of entrepreneurs.
1 If you jump, prepare to have 2 years of cash flow
In other words, if you’re thinking of leaving your job tomorrow, to start launching a business from scratch, it’s likely to take much more time than you expect to generate revenues (let along be profitable). Whatever amount you make in your company, you’ll realise that it’s very hard to do the same on your own at the beginning. So just calculate the money you need for 2 years, and make sure you have enough savings for these 2 years.
2 Jump only when you’re ready
Anything you can do to accelerate your path to profitability as an entrepreneur helps. Which means that there is much you can do while you’re still employed: meet people, work on your business plan, create contacts, develop a Minimum Viable Product, etc.
3 Educate yourself
Daniel’s answer below is very interesting: he managed to be paid once he raised money from venture capital. But there are a lot of other ways to get cash: awards, grants, subsidies, and of course sales! So best to know all about entrepreneurship before jumping - it’s hard enough for serial entrepreneurs, so put all the chances on your side.
4 Save, save, and save
Did you know that for $100 you can create your own website? Start a Facebook ad campaign? Use machine learning algorithms from Amazon?
$100 is an amount most people spend quite easily while in their jobs, but as an entrepreneur, you’d see how far this money can go. So if you want to be an entrepreneur, build your piggy bank…
5 Discuss - seriously - with your loved ones
Entrepreneurship is always difficult, and having the support of your loved ones is key. For example, if your spouse has a stable job, that could be a great timing for you to be an entrepreneur. If you’re both starting your venture at the same time, that might be a bit more challenging.
Of course, no two entrepreneurs are the same, and you’d have stories of people quitting their jobs and being instantly successful. But from my experience of having mentored dozens of entrepreneurs, and having myself launched several companies, is that cash takes time to come, so having savings help.
If you don’t have any savings, it might be best to wait a bit, build a cushion, and not put yourself in a situation where your money worries would really put a lot of strain on your project.