I’ve found that simple productivity techniques work best for me – the more complex the tool, the more likely they are to feel overwhelming and draining. The most helpful tools have been maintaining a simple to-do list daily and using the Pomodoro Technique (Wikipedia link) for short periods of focused work.
I’ve experimented with different lengths of time for the work sessions. Some people have suggested 45-minute or 90-minutes intervals for deeper focus. However, I’ve found that 25-minute intervals work better for me. It’s easier to fit them into a schedule, and it’s also easier for me to get started – the shorter time feels just a little bit less intimidating. When the break time arrives, I make sure that I stand up and look outside to avoid some of the physical drawbacks of staying seated in front of a screen for a long time. If the break is physical and sensory but without mental distractions (such as checking the news or other websites), I feel that I can usually keep my mind in a state of focus on the current project.
The Pomodoro application I have installed my computer keeps track of the number of work sessions completed by day and week. Recording these small accomplishments increases my mental energy, and on good days this can become a positive feedback loop: completing one session makes it easier to begin another.