This should always be the starting point when trying to transition a monolithic application to microservice-style architecture. Identify and pick up those parts of the application that are least dependent on other modules and have the least dependency on them, as well.
It is very important to understand that by identifying such parts of the application, you are not just trying to pick up the least challenging parts to deal with. However, at the same time, you have identified seams, which are the most easily visible ones. These are parts of the application where we will perform the necessary changes first. This allows us to completely isolate this part of the code from the rest of the system. It should be ready to become a part of the microservice or deployed in the final stage of this exercise.
Even though such seams have been identified, the capability to achieve microservice-style development is still a little further away. This is a good start, though.