I found a wonderful website with great information about gravestones. It had a lot of information, but I was particularly drawn to the part that shared how to look at an old stone and interpret it's history. Here is an excerpt, and at the end, a link to the complete PDF:

Interpreting cemeteries requires study on a variety of levels. While stone rubbings and photographs are important, it is also necessary to view the grave in the context of the entire cemetery and the cemetery within the layout of the town.

This tutorial will begin with the individual gravestones and work out. Studying gravestones is essentially the same as studying material culture. One must be able to view the stone in detail as well as in its entirety, and not overlook the importance of the most common features. Moreover, it is important to support your findings with other sources such as journals, diaries, and county and state records.

The following directions and questions will help you see the gravestone as a historical document:

-Read the writing on the stone.
-Look for names, dates, biographical information, poetry, inscriptions, and epitaphs, all of which are important to note and save for reference.
-What are you able to immediately conclude about the person memorialized by this marker?
-What language is the text?
-Look at symbols incorporated into the stone. Often, markers display symbols associated with age (for example, children's stones typically exhibit lambs), religious tradition, occupation, organizational membership, and military affiliation.
-Note the overall artwork on and of the stone. Early gravestones were carved in a fashion dictated by period fashion, local tastes, and the carver's ability. Therefore it is likely that you can piece together a chronology of style as you observe more and more stones. In some cases, small towns that traded heavily with large cities may have imported stones rather than carving them locally. The connection should be visible with enough observation.
-How is the artwork or style different of similar to those next to it?
-Was the design carved by hand with a chisel, was it carved by a machine, or was it etched with a new type of technology?
-Sketch the design in proportion to the entire stone and include the writing.
-What type of stone was used for the marker? Wealthy or important people in the community used expensive stones such as granite and marble, while the poorer folks may have used wood, lime or sandstone. -Government-issued military gravestones are uniform in design and made of marble, granite, or bronze. Military graves will be easy to identify.

There is a wealth of information if you click here.