I write off:
• Computers and software (depreciated over time)
• Internet connection
• Mobile phone bill
• Travel expenses (either mileage or wear & tear, not both) incl. parking
• Camera equipment (depreciated over time)
• Printing expenses and supplies (in and out house)
• Peripherals (printer, scanner, etc.) (depreciated over time)
• Sub-contractors fees (if I hire someone else to help on a job)
• Professional development training (classes I take, books I read, etc.)
• Food & Dining expenses (when I travel on business or for client meetings)
You can only deduct a percentage of these things, not the total cost. Be sure to get a well recommended accountant to help you with this. The AIGA or GAG can recommend one in your area.