As long as the expenses are legitimate then it's all good.
I just have a business on the side of my day job. Made about $50k last year in revenue but with a bit of accounting, came out with a loss of about $100 I try to make sure all my purchases are under $500 + GST so I can expense them, even if they are assets. A lot of the expenses just boost up my equity in the business as they're reimbursements. Then I can legitimately spend the equity I have to reduce it down each month. Means no income tax
There are grey areas of expenses that are still legal. E.g. if you go on a trip away, go visit a customer or something then claim half of the travel expenses as a business expense. If you're GST registered, make sure you get GST receipts for that stuff.
If you work from home, you can claim a percentage of your floor area used for business purposes. So if you use 10% of your house, you can claim 10% of your rent / mortgage (GST exempt) and 10% of your phone, 10% of internet etc. If you are an internet based business, you could legitimately claim more of your internet costs ... say 50%.