Be transparent – Your client wants to know where their money is going, so don't hide or be too general with line items on your invoices, and be prepared to show receipts. Otherwise, they'll wonder if you're padding the bill. Be specific. For example, instead of listing "materials" as a single expense, list each one on its own line, such as: paint, nails, plywood, etc.
Due Date: The Invoice Date plus Payment Term Days give you the Due Date, which is in plain English and easier to understand. Having a Due Date on the invoice is a tactful and professional way of making it clear to your customer when they should pay.