This is a big topic, and it’s great to read people’s takes on it. I guess the main things I’d offer are these:
Everyone works differently. Or more to the point, there are different ways of working, and what works for one person won’t work for everyone. This means try lots of tools, systems, approaches, and just use what works for you.
Don’t imagine you’ll ever have a system that’s perfect and it’ll last the rest of your life. Just see it as ongoing iterative improvement. And see that as something of interest, not depressing.
Tool-wise, I have two main things I use: (1) One is Todoist. Some people are list-oriented, others calendar-oriented. After I’ve spent time trying a heap of tools over the years, Todoist, which combines list and calendar in a solid manner, is the one I’ve used the longest, and the only “productivity” tool I continue to use. I won’t bore you with its benefits. I will say that like any worthwhile habit, it requires (and rewards) dedication. Oh, and while I have the paid version, the free should be fine for many people. (2) The other is a daily journal (in a markdown document, but any format would work). Every day I have categories of stuff (projects, health, home, etc.), and I note things in them of importance that I got done or need to retain some information about. Since it’s searchable on my computer, it’s a great outboard brain. I find having one such new document each month works well. (Quarterly got too long.) And I do them in reverse chronological order, so the new day starts at the top of the document above the previous day.
I read some GTD stuff, and the main things I retain from it, the main things I act on, are two: (1) Every day there is one thing that is the most important thing, and if you don’t get Thing 1 done, then even if you get Thing 2, Thing 3, and Thing 4 done, you’re not going to have a sense of accomplishment. (2) You’ll only get things done if you break them down into smaller pieces.
Work has a meta level. Work about work — organizing, planning, collating — has to be scheduled (has to have time allotted to it) just like actual project work.
And you have to take breaks. That’s not laziness, or procrastination. It’s healthy. Email isn’t a break. Stepping away from whatever you’re doing is a break.
I’m gonna reread what people wrote above, and I look forward to what else people contribute to this thread.