There is a genre of content out there that is obsessed with productivity systems. For a short while I was a big fan of this genre. I want to get things done, I want to accomplish tasks; if I implement these systems I could become prolific! I won't be so bold as to say all the productivity people are bullshitters; but there are smells. There is a common trap that productivity people fall into. A pattern of being unproductive in the goal area and very productive in executing, tweaking, refining, implementing, experimenting, discussing, and evangelizing productivity systems.
My system is this. First, work on the task every day. Second, at the end of working on the task leave yourself a hint as to where to pick up the next day. That's it in its entirety. The only thing that meaningfully helps me be more productive is preserving and encouraging momentum.
Here are three variations of this system in the context of a software engineering project.
Flavor 1: TODO NEXT comments. When using this approach I leave the occasional TODO comment in the codebase for things that stick out to me that may need work at some point in the future but not now. The TODO NEXT comment is the special one, there should only be one of these comments and you should add it at the end of a work session. Next time you begin working read that comment and giddyup.
Flavor 2: Next: commit messages. At the end of a work session the code is committed with a commit message that describes the change. At the end of the commit message is an additional line of text: "Next: benchmark changing the foo data from a list to a dictionary". I really enjoy this one in practice. Something about creating that last commit really wraps up the work session nicely. When you come in for the next session read the previous commit message and get started.
Flavor 3: Pen & paper. I've used all three approaches but writing things down is the most flexible and the most physically satisfying. I'm a sucker for stationary so your mileage may vary. At the end of the work session I write down a note about what to start working on next. When I sit down to work on the project again I read that note and get started.