Constraints make things interesting
This is a saying stolen and adapted from the splendid Paynter people. I talk about it in the Do Interesting book. And I've been thinking of it because I've been reading Inside The Box by David Epstein. It's about the fact that freedom doesn't make you more creative etc, constraints do. Relatively well-trodden territory but he has some good accompanying stories and he tells them well.
I was trying to think what constraints I use to make things interesting and I came up with these three examples. I'll confess, I've never made any of them stick as much as I'd like because, well, constraints are hard. But I still think they're worth a go:

Unusual word insertment
I used to have a challenge with a writer I worked with. We'd both give each other an unusual word and we had to try and get it into the copy we were writing each month. Webcopy, marketing emails, that kind of thing. No one else knew about it so the copy had to get through all the usual approval processes.
We didn't do it as often as we should, but it was joyously effective at making us think harder about our words. Once you get a 'tone of voice' in your head it's really easy to churn it out unthinkingly. Which is fine. But soon gets boring. Having to construct a bit of writing so the unusual word didn't stick out was a good constraint. It made us sound more human and caught the ear better.

Scheduled for monthly deletion
I like to ask web teams to delete something from the website every month. Just something. Whatever they reckon. Big or small. It makes people look out for the bloated and the unnecessary. Do we really need that FAQ? Is anyone reading that stuff about our mission? No one has ever noticed/complained about stuff we've deleted.

No more words for you
One of the major contributors to the planetary problem of document bloat is collaborative editing. Technology has made it very easy to add stuff but social niceties (and the fact that it's hard) make people very reluctant to remove things. So when sharing documents for thoughts/approval I try to say 'you can change whatever you like, you just can't increase the overall word count'. This used to go down very badly with the civil service. But it's a good constraint because it makes people much more careful about what they say. Do they really believe that their contribution makes the story stronger or is just a bit of drive-by randomness? And if you're determined to get something in, how do you express it succinctly, and what has to come out.
Video version: