step by step—gradually; little by little:
- You’ll be guided step by step through the process of taking your manuscript and turning it into a printed book.
step for step—
1. walking or riding evenly with another:
- Would you like a handsome dog that can match you step for step on long training runs?
2. keeping pace with smth.:
- You shouldn’t put investment dollars into anything but a mutual fund that tracks the market, step for step.