My greatest "productivity" improvement over the years is exactly this. Learning how to tell others (and myself) diplomatically "no". I used to take on, and create for myself, endless projects to "work on" and felt like I never accomplished anything. Paring down to the most important and fulfilling projects (and not trying to be everything to everybody) has improved things significantly.

I noticed myself doing this more and more, but not in the context of personal productivity, but rather in the context of "how can I help you help yourself". The gist is usually "can we solve this in some way that doesn't involve me coding a full blown technical solution". A lot of times, a workable solution is as simple as "just write 2 paragraphs about it in the docs" (and then mindlessly copying+pasting the link to it in chat until people get the message to just go RTFM). Or spending an hour doing a brain dump of the problem/solution space and letting them go off and do the work themselves.

Also works well for purchases