A microservice is not a service that has to be built from scratch. When you have a well-architected monolithic app already, avoid getting into the habit to build every new service from scratch. There might be opportunities to extract the logic from the monolithic service directly. Again, the above three principles should still hold.
Desire is the key to motivation, but it’s determination and commitment to an unrelenting pursuit of your goal — a commitment to excellence — that will enable you to attain the success you seek. — Mario Andretti