Time to GET PAID.
First of all, it is extremely important to remember to invoice your clients according to the terms in your contract. Invoices typically have to be paid within a certain number of days of being sent, so if you never send them, they never get paid! If you send them late, they get paid late, which can hurt your the amount of cash you have available!
You can generate an invoice either directly via your accounting software (e.g., Wave or Quickbooks) or using a Google template that you then upload into your accounting software.