I think of goals/sub-goals, tasks/sub-tasks, etc., along three dimensions:
1. Easy/Hard
2. Urgent/Not-Urgent
3. Important/Not-Important
Priorities then become clear:
Focus on the important and urgent first, typically tackling the easy before the hard.
Then focus on the non-urgent important items, but there you tackle the hard before the easy (and, more specifically, you break the hard down into easier parts).
Finally, but perhaps most critically, ignore to the greatest extent possible the not-important, especially the not-important that appears urgent and/or easy, as those items are the greatest temptations — and thus greatest impediments — to progress.
One Idea 