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

1. One thing at a time
   "They approached the complex project in a bit-by-bit manner";
   - in small stages, piecemeal, step-by-step, stepwise

See also: gradual