I like @lucasarruda's advice to have a high threshold of importance for what you allow on to your to-do list in the first place.
Of course that's easier said than done!
And I disagree with the admonition to just delete stuff that's been backlogged for long enough.
Well, I don't entirely disagree, just that it's not getting at the core problem.
Here's how I view the core problem, referring to my inbox, though it applies to any backlog (quoting myself from a Messy Matters article on proposed email features):
My email is dysfunctional. I keep things in my inbox because I can't afford for them to go
out of sight, out of mind -- but then that's exactly what happens. They get buried deeper
and deeper in my inbox by all the other messages I delusionally think I'm going to deal
with. It's a given that some things will fall through the cracks. I just need to make sure
I have some control over which things those are.
That's why deleting old enough items from your backlog misses the point.
You want more control over exactly which things you allow to fall through the cracks.
The above article suggests three features that email clients could use to help, namely:
- Snooze (make an item disappear from the backlog for a specified number of days, then reappear in the list)
- Re-Ping (make a new item automatically appear in the list in a certain number of days if a condition isn't met -- a reply, in the case of email)
- Auto-Expire (when an item first has your attention, set it to automatically disappear in a specified number of days, thus mitigating the painful slogs through the backlog, deleting obsolete items)
For email, I recommend followup.cc as a reasonable implementation of Snooze and Re-Ping. (Snooze emails by forwarding to, say, firstname.lastname@example.org to snooze for 3 days, and set Re-Pings by CCing or BCCing a similar address when you send an email.)
But, all of the above are just bandaid solutions for the real problem, which is getting yourself to work through your backlog and get it under control.
Here's what I do to solve that problem:
Namely, I'm literally forcing myself (using a commitment contract with Beeminder) to gradually reduce the size of my inbox by, on average, one message per day until it's down to a number I can see on a single screen.
Then hopefully I can just make it a habit to always get my inbox back to a screenful (or maybe I'll try for inbox zero) every time I open my email.
If it slips away from me again then I'll beemind it back down.
Disclosure: I'm a co-founder of Beeminder!