How should an invoice look in order to be professional and effective?

A professional and effective invoice should include the following elements:

1. Business name, logo, and contact information
2. Customer's name and contact information
3. Invoice number and date
4. Itemized list of products or services provided, including quantities and prices
5. Total amount due and payment terms
6. Due date for payment
7. Any applicable taxes or discounts
8. Clear and concise formatting for easy readability.