Don't wait until you're desperate to chase payment - by then you've already lost leverage. the hardest part isn't setting strict terms, it's actually enforcing them, so here's what actually works: require a partial deposit (usually 30 - 50%) before you start any work, then split the rest into milestone payments rather than one lump sum at the end. this way you're not fronting weeks of effort hoping they'll eventually pay, and clients take the invoice seriously when they've already given you skin in the game.
on top of that, automate reminders. send an invoice the moment work is done, then set calendar alerts to follow up 5 days before due date and again on day 1 overdue - keep it friendly but consistent. most delays happen because clients forgot or deprioritized it, not because they're dodging you. a quick "just checking in on this invoice from [date]" often gets you paid within days. if someone hits 30 days late, you can pause future work without being the bad guy - it's just business policy you enforce equally.