Healthy cash flow is the lifeblood of your business and it depends on prompt payments. Regardless of how you set up your payment terms, invoices are often paid two weeks late so if you aim to get paid in thirty days, make your payment terms around 15 days.
You need to do more than just sending an invoice. Set expectations with your clients before you start the work. List details clearly on your invoice and send it as soon as possible to the appropriate person or department.
Always keep detailed records of inventory and time and notify your client right away if there is a potential of going over budget.