Go to your library and see if they have a book called "Official ANA Grading Standards for US Coins". It shows pictures of all different types of US coins in different grades that you could use.
The very tricky part is if your coin is "uncirculated" - in other words, it has no wear at all. Knowing if a coin has a "little" wear or none at all is very difficult for non-collectors. The ANA book will tell you where the high points on the coin are, which is where the coin will first show signs of wear.
If it shows no signs of wear, then the grade is between 60 and 70, and is determined by the number and size of any small nicks, the coin's luster, how well the detail is struck, and the overall "eye appeal" of the coin. No book can help very much in that area. Also, on Franklin half dollars, it can be very important how well defined the lines across the bottom of the Liberty Bell are. If all the lines are visible and unbroken all the way across the bell, that matters a lot, especially on a 1953-S.
Chances are the coin is worth about $10. But just to tease you, a 1953-S Franklin sold for $69,000 a couple years ago (very high grade with Full Bell Lines). All you have to do is figure out if yours is the $10 version, or the $69,000 version.
