Check out this example: https://mikrocloud.com/blog/qos/tos-and-dscp.
For a more versatile way to prioritize important traffic without specifying traffic types, CAKE might be a better option. Check out this blog: “CAKE Configuration” and this thread: http://forum.mikrotik.com/t/fq-codel-cake-stories/181067/1
You might want to check out the preconfigured “cake-diffserv” options that are used to automatically prioritize and classify network traffic. In your case, “cake-diffserv=diffserv4” or diffserv8 would probably work better.