WordWeb Online

1. One thing at a time
   - in small stages, piecemeal, step-by-step, stepwise

1. A little bit at a time
   "the research structure has developed bit by bit"
   - piecemeal, little by little, in stages
    
2. In a gradual manner
   "the snake moved bit by bit toward its victim"
   - gradually, step by step

See also: gradual