If you can do it quickly, just do it
Saw this mentioned, thought it was worth seconding.
I first ran across this maybe twenty years ago, when I first read David Allen's Getting Things Done. It's part of his system for making sure no ball gets dropped while your task list remains manageable, but a small part, almost an offhand tip, doesn't really connect to the rest of the system.
Allen's version, paraphrased: when a task comes along, if you can handle it in two minutes or lest then do it right away. It seemed so reasonable and easy that I gave it a try.
First observation: a surprising number of tasks that sat languishing on my task list could have been handled in two minutes or less, often much less. And yet my habit was to put off everything, resulting in a task list where the large, important ones were buried in a clutter of small, insignificant ones — and I would give in to overwhelm, turn away from them all.
But once I started handling the tiniest tasks right away the list suddenly became manageable, grew slowly if at all.
Second observation: a change in mindset. When a new task came along my question changed from "Can I put this off?" to "Can I make this go away right now?" Rather than doing nothing but recording and sorting new tasks and taking satisfaction in that, I started just doing the little ones, then taking satisfaction that I hadn't added something new to my list. And the list stopped growing, or at least growing so quickly.
Third observation: the size of task I handled right away began to grow. What started as two minutes (barely) eventually became "Is this just too big to handle right now?" And too big became pretty big, in large part because I was getting a lot of instant gratification from actually doing stuff rather than putting it off. It put a very large dent in my habit of procrastinating.
Fourth observation: since I retired the stream of new tasks has slowed to a trickle, and nearly all of them are "just do it now" sized. So this habit now serves me well, enough that I don't really keep a task list anymore, the few things I can't handle right away are easy enough to remember.