为单元测试准备编码的最佳策略

I have a solution that is missing a lot of code coverage. I need to refactor this code to decouple to begin to create unit tests. What is the best strategy? I am first thinking that I should push to decouple business logic from data access from businessobjects to first get some organization and then drill down from there. Since many of the classes don't support single responsible principle, it's hard to begin testing them.I have a solution that is missing a lot of code