Managing a witness is a fairly time consuming task all on its own. Of course when have it running and it's chugging along it's fine but there are so many changes and future plans to be on top of, as we've seen with the most recent upgrades. And let's not forget about the cost, of course. That said, this is pretty much the baseline for all witnesses, so just maintaining the basic witness box package isn't enough. Here's my three:

1. Focus on the stability of the STEEM ecosystem. Deep understanding of all parts of the mechanisms like conversions, print rate, debt ratio, etc, witness settings... Upcoming things happening with resource credits, account creation, etc. There are quite a lot of toggles to play with, and we need to make sure we are careful with how that affects the whole economy.
2. Focus on any efforts that will bring adoption and keep retention, as that is really how steem will survive as an economic system. This does mean monitoring and taking a stand on how the reward pool is allocated. But also encouraging curation and community growth that help retention.
3. Focus on ways that the currencies can be used as a currency, e.g. value transfer. In part, organic voting already does some of this as we are effectively tipping for engagement (very roughly), but initiatives targeted at potential merchants I suspect are going to get us a big jump as well. Caveat: I don't count paying for votes here necessarily because it's an extension of the reward pool allocation.

On the side, I think bonus points for those running services that enable others to accomplish the three above would go a long way, so I'd look for that too.