Lots of good, practical, salt-of-the-internet advice from Brett Kelly on using OmniFocus. My favorite is "defer projects, not tasks." On some level of consciousness, I figured this one out a while back, and it's made my OmniFocus perspectives several orders of magnitude more sane.
I don't enter a specific date to defer entire projects. I simply set their status to "on hold," which keeps a placeholder for them in my project list, but keeps the individual tasks from fighting over my attention with active project tasks.
I think deferring projects also promotes a more project-oriented mindset. That is, it helps funnel tasks into goal-oriented buckets. If it's not obvious which project a task belongs to, there's an excellent chance that the task 1) isn't worth your time or 2) belongs in a more calendar-like medium like Reminders.app.
By the way, Brett just released a free OmniFocus book, too.