Don’t leave your job without a plan. Develop it in parallel with your current work. Insure that you are not moving into a field where your current employer has you signed to a non-compete agreement, a non-disclosure agreement or some other piece of paper you signed with your employment that would keep you out the business.
Then - follow your value system. Examine your talents, your attributes and your affinities and develop an idea for a business that you would enjoy.
Evolve your plan as you continue working for your current employer.
Give your start up idea the following test:
Do you have a product or service niche in mind?
Do you believe you have a market for 1 above and the means to reach it?
Are you willing to develop a business plan using the tool kit linked below to validate 1 and 2 above before you launch?
If the answer to the above questions is yes than take the actions indicated, observe the results, then make an informed decision on whether or not to proceed.
When you launch if your plan risk analysis indicates high early challenges, phase into them gradually while retaining your present employment. As the business matures and your risks are mitigated, cut over to full time and resign your old position when you are comfortable doing so.
Report Kenneth's answer
Great points, Kenneth. On the less tangible front, remember that failure is part of trying anything new. Even if you get knocked down, all that matters is that you keep trying by tackling in a different way. Being a life long learner with a passion will also serve you well.