When I want to make a quick miso broth, I use dashi packets that have no msg or preservatives in them. The above brand that I use is 1 dashi packet to 2 cups of water. You simply add the packets to water and bring to a boil. Then, reduce the heat to a simmer and cook for 3-5 minutes.
Once the dashi is ready, whisk in your miso paste. If you want to make 4 cups of miso broth, whisk in 4 tablespoons of miso paste. I like to use a sweet white miso but feel free to experiment with different kinds of miso paste to find the one you like best.
For a quick bowl of ramen, add the broth to cooked ramen noodles with some tofu, scallions, sesame seeds, and some Sriracha for extra kick!