A breakdown of services: If you're manually creating the invoice using Microsoft Word or Google Drive Templates for invoices, you'll need to include a breakdown of the services rendered and any additional charges associated with your work. Make sure to include a column for each of the following: description of work or services, date worked, quantity, rate, hours worked and subtotal. This makes it easy to tally up the total when you list out multiple projects or tasks you've completed for the client.
When you work out the contract with each client (and yes, you should have a contract in place!), you'll list out the terms of how often you plan to invoice and when you should be paid. For instance, you can agree to bill on the first of each month, or biweekly so you get paid every other Friday. Keep in mind whether your industry is one where you invoice upfront before any work has been completed. In this case you'll be detailing the progress of the project as opposed to doing a monthly invoice.