If I am going to develop implementation research using a qualitative method, which approach I may use? Or which approach I can consider in the design stage?
A lot depends on the accessibility of your sample. In particular, one of the main choices is between individual and focus group interviews, but focus groups can be harder to recruit because you need to get four or more people together in the same place at the same time. Another alternative would be dyadic interviews, where two participants share and compare their experiences.