mdmgrand,
Welcome to Treasure Net !!
For grading bills, I use The Official Red Book--A Guide Book of US Paper Money--by Arthur L and Ira S. Friedberg. The book gives a good grade description for bills in Gem Unc, Choice Unc, Unc, About Unc, EF, VF, F, VG and G. Of course, in addition to the distinctions given, one must consider (to use an old phrase): 'Beauty is in the eyes of the beholder'. Grading is a subjective decision based on individual biases and preferences. As you grade a bill, look for the obvious--and the obscure or 'covered up' aspects: Crispness, brightness, depth of color. Is the bill well centered? Have the creases been 'ironed' out? Does it appear that the corners have been repaired? If you hold it up to the light, can you see pinholes?
That should get you started.
Good luck,
Don.....
