Start by defining the desired outcome. If the goal is too big or too complicated, first define a smaller goal that is easier to achieve. By doing this you prevent your brain from triggering the alarm. Write it down. An accessible and clearly defined goal has a much better chance of being achieved.
You have already defined the problem—understanding the problem as a discrepancy between the real state of things and the desired one—. Now, what’s the first action you can take to achieve the goal? What might be the first step to take? Several things will come to mind, but only one is the true next step on which you must focus. That’s your next action. Write down the rest of the things on a list that you’ll put on hold, so that you’re not distracted by them.
Now you’ve started, you’re on the move. It’s the moment to take advantage of the inertia. Once the action is completed, retrieve that list of tasks and unresolved issues that you had parked, and choose your next action (or define a new “next action” if none of the ones you see is the right one).