This concept has been rehashed and changed into multiple buzzwords and agile this and that. At it's core though it's a basic concept of how to prioritize tasks.

At whatever level you are, when you're doing tasks or projects, the first thing you should do is identify (or try to find) the major risks first. What they are depends on the nature of your job. Here are some:

• Sysadmin - server needs backup mechanism
• Event manager - booking venue and invites
• Developer - key features required by stake holders, and then go by features that may take long development cycles
• Project manager - issues that will block key deliverables or cost overruns

and so on..

Everyone has to bear some amount of personal responsibility, even if you're junior staff. A common scenario is that you're given a project to finish at a set date, but before that date you're assigned random tasks so that you never actually get to finish it.

What you need to do is be aware of that initial responsibility, and when an adhoc task is assigned to you (that's life), you need to always weigh the priority against your key tasks to complete your project. Always be aware of that, and when assigned random tasks, negotiate and make aware of it to your manager. Most managers will understand and appreciate this, and help you prioritize, either by extending deadlines, or delaying the adhoc task, or reassigning it to somebody else. They'll also recognize your abilities to manage and deliver on projects, which means you're next in line for promotion.

For managers, what's obvious to you, may have been gained through years of experience. So it's important to share management skills with your staff. If you're a growing company, this will be a good base for expansion, as your junior staff start becoming junior managers.

Some more tips here: http://kaeru.inigo-tech.com/articles/time-management/managing-tasks/