Setting up clear terms of payment is a good start to setting payment expectations with a new client. A few days before you are set to hand over your deliverables, you can send a friendly reminder email notify that your work is almost done and you will generate the invoice soon. Follow up your professional invoice reminder with a couple of late payment follow-up emails till the due date. However, even if the client is well-meaning and wants to pay on time they may get delayed due to several factors which may not be in their control.  If a client is genuinely professional and misses a payment once or twice due to some issues, understand their inconvenience. But if a client consistently delays payments then it is a mark of their reimbursement process. Look out for red flags like this and safeguard your business by avoiding work with such clients.