You can either check in your select statement or in code. In SQL:
SELECT IsNull(FirstName, 'N/A') as FirstName,
Coalesce(LastName, 'N/A') as LastName, Date FROM EOI WHERE (FormID = '13');
In .Net, you need to compare it to DbNull.Value:
Label1.Text = reader["FirstName"] == DBNull.Value ? "N/A" : Convert.ToString(reader["FirstName"]);
Note that in the above example, Convert.ToString() will convert nulls to empty strings. This is a third example of what you can do.