Starting is easier when the next action has fewer words than the excuse for postponing it.

Postponement usually comes with an elaborate story: the conditions, the timing, the preparation still required. If the reason not to start is longer than the description of the first step, that imbalance is the whole problem. A step small enough to say in five words is hard to argue with.

Write your next action as a short phrase: open the file, put shoes on, send the one line. If it takes a full sentence to describe, it is not small enough yet. Cut it until the excuse looks silly beside it.