I'm on my 1st revision.

Just sent out a revised billing policy @ the beginning of the year as I was not implementing any real set procedures other than "due on receipt". lol
My new terms, which I stated will be effective March 1, are as follows (not verbatim):
1. due on receipt - though...
2. pay by 1st of month following receipt of invoice (this is pretty lenient I know)
3. outstanding balances will incur 1% late fee each month invoice remains open (on every open invoice)
4. if no payment by 1st of month following receipt of invoice, in addition to late fee, work will be suspended until resolved.
I'm so not an accounting person, so these are just my initial guidelines I'm putting in place - & I imagine they'll change over time. I too accept PayPal or CC's via PayPal, & checks.