My experience is that it helps to:
A) Have a routine.
B) Write it down.
C) Finish something every time you start.
With a good routine, a great many decisions you would think about are already made. Unless you work in a factory, your first day in a job or role will be far from routine. Here are some suggested attributes for the routine you invent.
- Your routine can be blindingly simple, or startlingly complex. It must be logical for you, and permit an efficient flow of work inputs to work outputs.
- Your routine should aim at fluency and velocity. If it feels wrong it probably is wrong.
- Your routine should be practiced mindfully because on autopilot you will not find opportunities for variation and improvement.
Every job I have had, needed a different routine, and usually I struggled with no routine or with a partial routine until pain forced a change. Much of the important leverage is on what you choose to do daily. I believe it is very important to follow both a personal and a team process.
Write It Down
When you write things either on paper, whiteboard, or electronically, you effectively extend your memory outside your allotted share of gray matter. If writing things down is not part of your routine, change your routine.
If you record a plan, either sketched or refined, before you begin a project or task, there is a reference that can be marked to show completed items. This works particularly well if you work through your plan in sequence. When the work is interrupted, you already have a map you can use to resume it. Rarely will a circumstance or person wait for you to log your progress and plans. If you are lucky (and smart), you can reserve the last 15 to 20 minutes of the work day to update your map.
Finish What You Start
Clutter and confusion abound where tasks are begun without regard to finishing previous tasks. We are increasingly dependent on collaboration, and techniques like Scrum and Kanban are highly valued in some work environments because they accelerate collaboration from a random whenever to something that is facilitated by the team once per day.
Forget about milestones and percent complete. On a project a mile can take months. We can subjectively allocate percentage complete, but too often, when the percentage is 90%, people often find they are a mile offtrack and that it is another painful 90% to get it done.
Work needs to be defined in inch-pebbles. "Inch pebble" is a term that is used in the literature, and an internet search would find many descriptions. We need to dump percentage complete. We need to judge our task as objectively as possible, making a decision that it is done or it isn't. The cost to comeback to a task can be very high, so defining a subtask in such a way that when it is done, it never needs addition attention is very powerful.
Additionally, if the pebble can be made to fit in a time box, we can go from needing weeks of focus on one thing, to a day or an hour. Define the work that needs to be done in a granular fashion gives us a lot more flexibility in handing off work to a pipeline, to doing like tasks together in a block, and to demonstrating progress early and often.
A neurologist might be more definitive, but I think that a task that has the advantage of being begun and finished in a single sitting, or within the space of a single day, has the advantage of being loaded to short term memory without the costs of being recalled from long term memory. Similarly, I find as I work a task, often I gather more materials, equipment, creative work product, and documents together until there is a critical mass that lets me complete the task. A task that spans small or large interruptions may requires this time consuming gathering to be done more than once. When you define your work, find efficiencies that let you load your brain/desk/work area just once.
Hope this is an effective suggestion. Good luck.