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.
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.
A Lincoln Memorial Cent is difficult to grade in the higher MS grades like MS65 and above, 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 for contact marks is the high points of the hair, beard and the lower shoulder. Sometimes these marks can't be easily seen without a 5x jeweler's loupe, so when grading Lincoln Cent, pay close attention to these areas.
Furthermore, before a Lincoln Memorial can attain the MS67 grade or above they must have fully struck details.