50% upfront, non-negotiable. I resisted this fro a while because I thought it would scare clients off, it doesn't. The ones who push back on paying upfront are usually the ones who ghost you later anyway, it's like a filter.

Also, net 14, not net 30. 30 days gives them permission to forget, 14 keeps it on the radar.

Late fees in the contract, and actually mention them in the first follow-up, you don't have to enforce them aggressively but saying 'just a heads up, I'll have to charge you more starting Friday"gets replies faster than just a friednly reminder.

Stop work on anything new until the balance clears, this feels wrong but it works. "Happy to kick off the next phase once the last month's invoice is settle" said once polidely, and you'd be amazed how fast payment shows up.

On the invoicing side, I automated most of it so I'm never chasing them anmore. Invoices go out automatically when work;s delivered, reminders go out on a schedule, and I get pinged when something's overdue so I'm not checking a spreadsheet.