Set aside enough cash to cover at least two months of expenses. When you’re earning well, move 20% of each payment into that account and leave it alone.
For unpaid invoices, I enforce late fees after 30 days and halt all work after 45 days. Stick to your guidelines. The clients who value your time will pay on time. Those who don’t are not worth your effort.
Always take a deposit upfront, even if it’s just 25%. That way cancellations don’t hurt as much.
For unpaid invoices, I send reminders every week after the due date. First one is friendly, second one mentions late fees, third one gets firm about stopping future work until they pay.