There are a few things to notice about a family Bible as part of your research. When was it published? It is sometimes a custom to write down family events in the Bible. Perhaps family birthdays or weddings. Match the date of the publicity of the Bible with these events. You will be able to tell whether or not the dates written in the Bible were recorded when they happened or at a later time.
Carefully study the handwriting of the entries. Do they looks as though they were written by the same person? Are different inks used? Is there an inscription?
Thumb through the Bible carefully to note if any other notations were made. Some owners underline certain passages. What is the meaning of the passage? Perhaps a notation will indicate it was used at someone’s funeral. Also it is common to find other papers saved in the family Bible. Sometimes these are original records of birth certificates, obituaries, or handwritten notes.
If you don’t have a family Bible in your possession, check the library to see if one was donated. The Library of Virginia, for example, has over 6800 family Bible records in their possession.
As you can see, there is a wealth of information to found in family Bibles! They are well worth giving a look.