Get a stack of blank index cards, like these from amazon. First thing in the morning take one and write down three things to get done today. It’s best if these things are steps needed for some larger goal.
Then do these things first before any other work, including email. Use a big sharpie, and leave the card in plain sight so that it’s visible all day long.
This is low tech, but it works. It’s pleasing to check things off. It’s also pleasing to throw the card away at the end of the day, and start fresh tomorrow.
As a bonus, keep the back of the index card blank. If you notice yourself taking too long to make a decision, write it down. Make the decision before moving on to the next thing.