Invoice details: Across from where you put the recipient's name and contact info, include the details of your invoice. This placement makes it easy to keep track of vital information — for both you and the recipient. It doesn't matter what kind of numbering system you use, just make sure it's in sequential order so you don't get confused.
Use a digital format – Using a digital format is one way to ensure your invoice is professional, and to indicate that you're likely to use the latest tools, and follow best practices, on the job. Simple mobile apps like Invoice2go will allow you to create and send professional estimates and invoices on site when the project is still fresh in your client's mind. These apps can even store receipts so you have a real-time way to keep your expenses organized for easy presentation to your clients.