Simple yet profound.
As you finish up your design today, take a moment and ask yourself:
"If I had another hour, another day, another week to work on this, what would I do differently?"
Then write that down. Is it possible to incorporate those ideas into your current design? If the deadline doesn't permit any additional changes, you might want to consider keeping these ideas on the back burner in case you need them for future concept updates and changes.
In today's deadline-driven society, we as designers must struggle to avoid falling into the "production" rut that can easily occur when we feel rushed or too busy.
Sit down, relax and think through your next assignment!