Building certainty to leave my job for my business

I have recommitted to leave my job by April 2022. I kept renewing my work contract due to a lack of certainty in myself and my ability to sell/earn on my own. I’ve been holding myself back from work distractions and not taking action in my business. In April, I’d like to have built enough certainty in myself and my business to finally take this leap.
1. What study vault resource would you recommend to build certainty
2. Any practical business advice I should consider that will also help me build this certainty