This is an on-going lesson in watercolor. See the previous posts for more.
Set the piece against a wall and walk a distance from it. Look at the values. Do you see a wide variety of darks and lights? Are they in the appropriate places? Hold the painting up to a mirror to see it with fresh eyes. What areas do you need to correct at this stage? Have you worked around the entire painting or have you worked only in some areas, leaving others lagging behind?
Note the areas that you need to work in to catch everything up to the same stage and go back to develop those areas. Be careful not to overwork any area of the painting. This will give it a fussy look, instead of a crisp, completed look.