Assess your situation
First up, you need to work out how much time you can actually commit to your new business and how much money you're going to earn from it.
You might be in a situation where you can dedicate all of your time to the business, or maybe you're just going to do it part time, or even seasonally. You pick what works for you.
You can carry on working full time while your new business is just getting off the ground. In fact, lots of people carry on working before they plunge into self-employment.
The downside is that you will have to work pretty long hours, the upside is that you can get the cash flowing in before you quit your job.