I'm working on a painting that is rather panoramic in scale. It needs to show a great deal of depth, as well as breadth.
A painting like this cannot be rushed; it needs constant re-evaluation and pondering. The painter must ask the following questions:
Are objects in correct scale?
Does the background fade into the distance as it should?
Despite the grandness of the composition, is there still a focal point that is well defined?
Is there enough detail in the foreground to be believable?
Is the sky as dramatic as the scene would demand?
So I recommend that you stop at the point where you know the piece is nearly done. Don't look at it for several days. Then get it out, put it on the easel, and look at it using a mirror. This will help with the scale and depth issues. Squint at it for a while. How are your values? You should have variations from light to dark with no heavy emphasis on any one tone. Still with your eyes squinting, is the focal point readily seen? If not, adjust the contrast and juxtaposition of warm and cool colors to really make it pop.
Then, armed with your new perspective on the subject, make some subtle corrections and Voila! you are done!