It turns out that I was already doing most of them pretty well. For example, offlineimap only downloads new mail every 30 minutes, so I don't constantly waste time checking my inbox for new mail. And I'm pretty good at deleting mail I don't want, quickly sending quick replies to easy mails, and adding calendar entries for time-sensative mails. So my inbox was only 90 messages long..
The main thing I need to improve seems to be getting out of the habit of leaving deferred things to sit in my inbox. I went through and about 80% were mails sent from the Debian BTS. All that stuff is in the BTS, so there's no need to keep it in my inbox. Another 10% should have been in a BTS, but was sent directly to me -- so I put it in the BTS, and removed it from my inbox. I know I'm not the only one with this problem, BTW.
I recommend watching the talk. Thinking about mail in the inbox as only having one of 5 actions you can perform on it (delete, defer, delegate, respond, do) really helps process it quickly.