microsoft.public.access.forms

Hi everyone,
I am just setting some rules for my form via code and was in need of some
advise/help. I have coded the following:
Private Sub Form_BeforeUpdate(Cancel As Integer)
If IsNull(Me.First_Name) Then
MsgBox "Please enter the your first name", vbCritical
Cancel = True
First_Name.SetFocus
End If
End Sub
If I wanted to add addional fields to check if they are empty before the
form closes let say received date and zipcode, how would the code change?
Any help is apprecieted.