I like to do an end-of-year email cleanup, to find any emails that are making it into my inbox despite all my filters, so that I can create new rules/filters to catch them. This project was helpful for me, too!
When I looked at my latest messages I realized there are a few new rules I need:
Something that puts my followup.cc reminders in a place I can review them once or twice a day, instead of as they arrive
A rule to move shipping notifications to my end-of-day file so they don't distract me
This will be trickier, but there are some boiler plate marketing emails that I get regularly -- usually asking me if I'll take guest posts on my blog. I am going to try filtering out "guest posts" if I can find another keyword or two to make sure it doesn't catch stuff from actual humans.
You may also notice that some of the items in my inbox also have labels. That's because some of my mail rules apply mail labels to categorize messages, without removing those messages from my inbox. I'm going to review the mail rules that apply those labels to see if I want to make some of those messages skip the inbox altogether.
What have you noticed as you've worked on your projects? I'll look forward to seeing them.