Having gone through film school and seen both good and bad editors in the learning process, I can also say that one of the main killers of beginner editors is that they think only in terms of a final product. If a cut doesn't work, they think the film is tanked. I learned early that "firebombing" an edit, radically changing the structure of a film that isn't working, can be very productive. When you're trying to solve major problems, for example exposition or overall pacing lag, it's often good to recut certain scenes from scratch rather than just change what you already have. That way you kill the preconceptions about how those scenes and that cut. (This approach probably works best for narrative film and documentary, and less so for limited-footage, semi-narrative pieces like commercials.) It's also important not to abandon an idea until you've worked it to its potential.