I added a couple of ideas to the idea section of the webinar during the live event 
. Here are some other ideas:
I usually go through once a quarter and shut down old campaigns/archive. I do it myself since I find it soothing 
but it's also a great thing for an intern to take on (provided you trust that intern).
My old instance relied heavily on inherited tokens so I would review those a few times a year to make sure they were still relevant to what we were doing (soooooooooooo easy to put into a place a new process and forget things like this, creating confusion and clutter).
Once a year I tried to clean up design studio images/irrelevant forms/old templates (scary, I know) and did one project with the Design team where we completely refreshed our images and implemented the most beautiful naming conventions I have ever seen.
Analytics can sometimes get cluttered with a million very specific reports (2015-Email Report for EMEA <--example) so removing those or figuring out if they're actually used/needed is great.
Also, since it's just us friends here in the circle of trust, having a 'read only' user role or maybe 'analytics only' and if someone hasn't logged in for 30+ days and they aren't OOO/on leave, moving them to that role to see if they scream. If so, they must be using the account sometimes...if not, they aren't really using it, are they? Or if they are supposed to be using it and aren't I'd use that as a time to plan my next quarter or two of training
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