Monitor your motivation and energy levels. If high, work on a premium task. If medium, work on urgent or important non-premium tasks. If low, work on a fun task or take a rest. Train yourself to be “rewarded” with the completion of a task.
Don’t let the inability to perform a big task get you down – channel the frustration towards executing smaller tasks, thus clearing your plate and building up some momentum for when the time is right to tackle the big task again.