It can be tempting to display as much data as possible on a dashboard, especially when a system like Prometheus offers the ability to have such rich instrumentation of your applications. This can lead to consoles that are impenetrable due to having too much information, that even an expert in the system would have difficulty drawing meaning from.
Instead of trying to represent every piece of data you have, for operational consoles think of what are the most likely failure modes and how you would use the consoles to differentiate them. Take advantage of the structure of your services. For example, if you have a big tree of services in an online-serving system, latency in some lower service is a typical problem. Rather than showing every service's information on a single large dashboard, build separate dashboards for each service that include the latency and errors for each service they talk to. You can then start at the top and work your way down to the problematic service.
We have found the following guidelines very effective:
If you find yourself exceeding these, it could make sense to demote the visibility of less important information, possibly splitting out some subsystems to a new console. For example, you could graph aggregated rather than broken-down data, move it to the right-hand-side table, or even remove data completely if it is rarely useful - you can always look at it in the expression browser!
Finally, it is difficult for a set of consoles to serve more than one master. What you want to know when oncall (what is broken?) tends to be very different from what you want when developing features (how many people hit corner case X?). In such cases, two separate sets of consoles can be useful.