Incremental Numbering

I am trying to set up a workbook that will print a blank invoice which will automatically increment the invoice number (in this case cell G2). I have been trying to use the "Private Sub Workbook_BeforePrint(Cancel As Boolean)" code, but cannot get it to work, and also tried to make a Macro, which worked but would increment by two rather than one but only print one, so that there was a number missing. The purpose of this is to be able to print out blank NCR sets to be filled in for use with customers in the field.
Any help greatly appreciated

That addresses a different problem. I don't want to keep copies of these invoices as Excel files I just want to be able to print them out without having to change the invoice number every print.