I’m not much of a productivity system guy. But GTD has some good ideas that I’ve tried to adopt:
Breaking down tasks into actionable steps
Separating things out that really have a firm due date from those that really need to be taken care of but not by a specific date
I also keep a maybe someday list of things that may never happen and may outlive there being a good reason to make happen. I did what I liked to refer to as a value renovation project on my house this summer and there were a number of projects whose cost and/or effort just exceeded their utility.