When you have a complicated or big task to complete, inertia can manifest. Break the complicated or big task into small pieces, and begin one of the smaller tasks pronto. If it helps, change the location where you are working.
You want to avoid getting in the day-dreaming mode, in which you are either completely side-tracked or left asking the question: “where do I begin?”
The key is to get in the rhythm of completing tasks in smaller pieces. Once the rhythm is established, you will find a much smoother flow of productivity.