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.
While you can make up your own invoice or use a free template, it's often easier to use an invoicing system that offers more in depth features. Some invoice systems, like Harvest, offer the option to create estimates for big projects, keep track of multiple clients and send reminder emails when payments are late. Another option is Freshbooks, which offers similar features but includes profit and loss sheets, as well as trackers to help you manage your time. Both of these services can be used for free or upgraded for a small fee, and include lots of other cool features, like scanning receipts for work completed in the field.