I use the Goldmine visual grading standard. Grading is record/cover.  (i.e., "NM/VG+")

 
Grade
Record
Cover
Mint (M)
A Mint (M) record should appear to have just left the manufacturer without any handling; that is, it should appear perfectl No scuffs or scratches, blotches or stains, labels or writing, tears or splits; nothing.  And age has nothing to do with it; the same standards for Mint apply to a 10" soundtrack fmm 1954 as they do to a 'grunge' album from 1994! A Mint album cover should appear to have never had a record in it; no ring-wear (defined here as any imprint on the cover from the record that it formerly held), dog-eared comers, writing, seam-splits.  Uh-uh.  Mint means perfect and nothing else.
Near Mint (NM)
.  A record that is otherwise Mint but has one or two tiny, inconsequential flaws that do not affect the play is Near Mint (NM).  For many, NM and Mint-Minus mean the same thing. (I prefer NM.) Covers should still be close to perfect with minor signs of wear or age just becoming evident: slight ring-wear, minor denting to a comer, or writing on the cover should all be noted properly.
Very Good + (VG+)
Sometimes referred to as 'Excellent," a Very Good Plus (VG+) record has been handled and played either infrequently or very carefully.  That is, an item obviously not perfect, but not too far from it.  On a disc, this could mean that there are light paper scum from sliding in and out of a sleeve or the vinyl may have lost some- not all- of its original luster.  A slight scratch that did not affect play in an otherwise NM disc would be acceptably VG+ for most collectors.  A scratch of any sort that audibly clicked throughout the music would not be acceptable.  Some wear from storage is acceptable, especially light wear that does not affect the beauty of the artwork. 
Very Good (VG)
Very Good (VG) records will display visible signs of handling and playing, such as loss of vinyl luster, light surface scratches, groove wear, and spindle trails from countless spins on the turntable.  A VG record looks like it will have some audible surface noise when it is played, although any such noise should not overwhelm the musical experience.  VG records should appear to have been wellplayed although well-Ioved by a responsible owner.  Gouges in the plating from slapping the disc down onto the spindle, rips in the label from pulling stickers formerly afflxed, etc., are all unacceptable. This is a difficult grade when discussing paper goods.  Like a disc, usually a cover is VG when a variety of problems are evident: ring wear, seam splits, bent comers, loss of gloss, stains, etc.  An aggravated combination of two of these problems- never all of them- would likely cause a sleeve to be graded VG.
Good (G)
Good ('G') in record collecting parlance all too often means a beat, trashed, take-it-to-the-flea-market frisbee.  Good should mean that the record is well-played with any number of defects that collectors normally shy away from, such as an almost complete loss of surface sheen, aggravating surface noise, etc.  Still, the purchaser, knowing full well that he or she is buying a Good record, should be able to take it home, slap it onto the turntable and have a good time listening to it.  Records that do not provide this most fundamental requirement are just no good.  A Good record should conunand 10- 15% of the NM price. A Good cover has seen considerable handling over a course of years and displays the obvious signs: ring-wear on the cover; some seam-splitting, particularly along the bottom, which would receive the brunt of the record's sliding in and out; corners may be dog-eared to a light degree; an infatuated owner may have written his or her name somewhere; etc.  If a record or cover is beneath your contempt, it is not in 'G' condition; look below for the appropriate grade.
Poor (P)
Basically, junk.  Also junk.