Disclaimer: This is just a guide to give you an idea of what your coin might grade. Often coins will grade higher on one side vs. the other. In example, it's possible for a coin to grade G4 on its obverse, but grade VG8 on its reverse. Also, this guide is not a claim that one's coin will obtain any grade listed if submitted to a third party grading service.
Some photographs are posted under the Fair Use doctrine of Copyright Act of 1976, 17 U.S.C. § 107 for the purpose of criticism, comment, news reporting, teaching, scholarship, or research.
This guide makes the use of obverse pictures as grading examples because U.S. Lincoln Cent have two different reverses (Wheat Stalks and Memorial), and each of these reverses have different diagnostics for grading. However, the obverse is the dominate grading surface and will suffice in giving a guide only view to get a general idea of a grade. Furthermore, your coin might look like the picture, but will grade a point to differently. Remember, this is just a guide.
Along with a grade, Lincoln Cent also come with three other designations, BN (Brown), RB (Red-Brown), RD (Full Red) with the R being the most desirable state of preservation for normally toned cents. Below are examples of each state of toning.
MS64 RD (RED)
MS64 BN (BROWN)
The war-time cents where made of steel and can be picked up with a magnet. Many collectors and dealers have plated or coated other "copper" dates with mercury or zinc to make them look like a steel cent, but the magnet trick will reveal the fakes.
A Lincoln Cent is difficult to grade, but one aspect of grading the MS grades is in the smallest of details. Many cents appear mark free in the fields, but a few places that's often over looked is the high points of the hair, beard and the lower shoulder. Sometimes these marks can't be readily seen without a 10x jeweler's loupe, so when grading Lincoln Cent, pay close attention to these areas.