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.
Fully struck examples with Full Head details bring the most premium. The head is the most weakly struck area of the Standing Liberty Quarter. Other areas important to grading is the high points like the shield and shield rivets, the robe over the midsection, Liberty's left knee and thigh above knee on the obverse.
The reverse high points is the front part of the eagle's wing and feathers.
The more wear in these areas the lesser the grade of the coin, and absences or flattening of these features, due to circulation wear, reveals and even lower a grade.