Besides getting an accountant and setting an initial meeting, get a good bookkeeper to come every month. He or she will be able to keep track of expenses, including gas. If you are working from home you will be able to deduct a certain portion of your computer, power, mortgage interest (or rent), phone, internet, etc... as business expenses.
As another poster said, if you make over $30,000 a year in revenue, you must register for GST - that is, you must collect GST on all your sales. However, you are also able to get a GST refund on virtually all of your business expenses as well. So if as another poster said, you pay $300/hr +$21 GST to meet with an accountant, if you are registered for GST, you will get your $21 back from the federal government. An accountant and bookkeeper can help with this.
Finally, check-out Canada Revenue Agency's website. It has lots of info for small business owners at
www.cra.gc.ca
Oh, you may want to consult with a lawyer as well. I don't know what arrangement you have, or what contracts you have, but speaking with a lawyer is always a good thing. You may wish, for example to enter into a contract with the person you are working for, or for that matter, the person you are working for may enter into a contract with you. Get it checked-out.