Here is a small but annoying personal flaw of mine: I feel at my most productive when I don’t have many tasks left on my to-do list. That means that I tend to want to do the small, easily-accomplished tasks first, instead of the larger (but more important!) ones. You can see how that might be a problem.
The best thing to do is the “one big thing” approach, but as I’m tackling the one big thing, I find myself often distracted or stressed by the knowledge that I have a lot of things still left to do for the day, even if collectively those things are only maybe an hour’s worth of work total.
So sometimes, I cheat. I trick my brain a little.
When I’m writing out my to-do list for the day, if it has both a single large task that needs to be done, and a decent number of smaller tasks that I know will distract me, I’ll put a few things on the list that are actually already done. Small tasks that I actually did the night before or that only require 10 seconds of effort, like “check the mail.” The effect of this is that as soon as the day starts, I can put 3 or 4 checks on the list, and that gives my brain a sort of false sense of momentum that lets me focus on the big task without getting distracted by the smaller ones, because it feels like a lot of the smaller ones have already been accomplished.
I can’t do this too often, or my subconscious will build up a resistance to it and it’ll become rote. But every once in a while, it’s a helpful little trick.