Keep a list of things you need to do. As new tasks come up, add them to the list. When you finish a task, cross it off the list. Then ask yourself, "What's the best use of my time right now?" Find the task on the list that answers that question and do it next.
See: "If You Don't Have the Time to Do It Right, When Will You Find the Time to Do It Over?" by Jeffrey J. Mayer