You MUST know these interpretations of Canadian tax law, or you must give them to your accountant. They help you maximize your tax credits, minimize your taxes payable and explain repeat annual losses (if you have them).
Bulletin 504R2, “Visual Artists and Writers”
Bulletin IT514 “Work Space in Home Expenses”
Bulletin IT473R “Inventory Valuation”
There are many other interpretation bulletins that may be of interest to you at the CRA Site (claiming car expenses, claiming support payments, etc) depending on your circumstances.