If you charge by the hour, provide an invoice to clients. Break down all charges. Here’s an example.

Fees for professional services rendered:
Meeting on April 4, 2013 to discuss retirement planning matters $X
Review of investment portfolio statements, telephone and email communications on May 17, 2013 $X
Total Fees $X
Disbursements:
Postage and/or courier, photocopying and other direct costs –
Total Fees and Disbursements $X
Goods & Services Tax – 14% $X
Balance Owing $X

Source: Blair Corkum, fee-only advisor at Corkum & Arsenault