you can really get caught up in a paper trail that equates to unbillable time but could save you butt. For out of town clients the lengthy version is this: they call, I send an estimate/quote (your established price), they send a purchase order number (their committment to pay), (ya do the work) send an invoice based on the PO#. Still may take 30 days to get paid, but you have recourse. Your invoice can be basic as already stated, but with an acccounting program like Quickbooks, all this is easy to create and track past due stuff and create monthly statements, etc. And if you’re going to email invoices, be very clear that they should pay from what you email. Most take it that its a copy and will wait for a hard copy. And there is a difference between an estimate and a quote( although i’m not an attorney): estimates are open for revision, quote is a fixed price.
I know another post said not to include your SS#, but I try to head off the 60-90 day issue by sending a completed W-9 Taxpayer ID form with my invoices (get it here https://tinyurl.com/bskds) This way, at 30 days you don’t get a letter stating you need to provide it, and then they pay in another 30 days. The latest delay I have (from a regular client no less) is to fill out a vendor profile, just another way to delay things.
May sound pessimistic, sorry. 99% of my business dealings are smooth and painless, you just need to be professional and establish a good groundwork from the start. If they see you as a pushover, you get paid last and they treat you as an amateur. The squeaky (but polite) wheel gets the oil. As stated in many other threads, its all about relationships – deliver a good product, they want to keep you as much as you want to keep them.
Steve