Knowledgeable people in TDD code faster and better using the technique. Practice takes you there.
In the mean time, test the parts of the application that do not change. How much can the payment flow, sign in or sign up change? Make sure you have test for those in order to catch regressions.
Know where you are. Are you building to last? Are you building to test an idea? balance.
Build better abstractions.
Practice. Practice. Practice.