I am not sure of what other freelancers do to process their invoice. Because everyone has a unique experience and every client is different! I believe in having a proposal sent out before starting off with any client. That proposal should have all the discussions, payment discussed, deadlines, scope of working, work hours and almost everything to avoid the last minute hassle. The major steps you should take to bill your clients are. Have a unique invoice number. Don’t use the same invoice number for every next client. Include all information about the proposal on your invoices. Do not forget including invoice date and payment due date. Specify payment options- whether you prefer cash, a cheque, a credit card or a service like PayPal-so your client sends the payment to the right place. Mention required timeline along with charges for a late fee for invoices that are paid past their due date. Last but not the least, have a breakdown of the services rendered, so the client knows exactly what t’re paying for. Bonus tip. Use an invoicing tool to simplify/automate the process. Hope this helps. Thanks!