Prioritize: The key word is prior.
It's about taking action on that which you've previously determined to be important.
My daily goal is to define one major HVA and then 2 additional important HVAs.
A successful day (+10) is when I make progress on HVAs before 3pm. By 3pm, my energy is usually spent, so it's how I spend the first half of my day that matters.
If you don't have any priorities (or if everything his a high priority), how can you have conflicting priorities?
Until you see the distinction between what's important, unimportant, and tyranny of urgency - you will never get a handle on priorities.
It's not that everything is important
Both our and our customers' needs change fast. If something was marked as high priority two months ago it might not be that important anymore. Before starting to work on a task like this ask yourself: Is this still a high priority?