Regardless of what you do you want to be professional about it and if you quit your old job because you hated it then there are definitely some tips when it comes to building your own business...
1) Do what you love!
You aren't going to enjoy this new role of being self-employed unless you really love what you are doing. After all, you hated your old job - why would you switch to something new that you will hate anyway? You're going to devote a lot of time and energy to starting a business and building it into a successful enterprise, so it's really important that you truly deeply enjoy what you do.
2) Start your business while you're still employed
How long can most people live without money? Not long - unless the business you are making involves growing/hunting/fishing for food. And it may be a long time before your new business actually makes any profits. Being employed while you're starting a business means money in your pocket while you're going through the early stages.
3) Don't do it alone - Get a business partner if possible!
If you can't find a business partner at very least you need a support system while you're starting a business. A family member or friend that you can bounce ideas off and who will listen sympathetically to the latest business start up crisis is invaluable. Even better, find a mentor or, if you qualify, apply for a business start up program. When you're starting a business experienced guidance is the best support system of all.
4) Get clients or customers first
Don't wait until you've officially started your business to line these up, because your business can't survive without them. Do the networking. Make the contacts. Sell or even give away your products or services to gain reviews. Start marketing immediately and always be ready to impress a potential client.
5) Write a business plan
The main reason for doing a business plan first when you're thinking of starting a business is that it can help you avoid sinking your time and money into starting a business that will not succeed. Have other people look over your business plan and look for gaps / ways to make it more profitable.
6) Do the research
You'll do a lot of research writing a business plan, but that's just a start. When you're starting a business, you need to become an expert on your industry, products and services, if you're not already an expert. Learn what your competition is doing. Joining related industry or professional associations before you start your business is a great idea to learn whatever everyone else in the industry is doing right - and what they are doing wrong.
You don't have to be an expert on everything. If you're not an accountant or bookkeeper, hire one (or both). If you need to write up a contract, and you're not a lawyer, hire one. You will waste more time and possibly money in the long run trying to do things yourself that you are not qualified to do.
eg. Get a professionally designed website by a local Toronto website designer. And get local SEO so you can advertise your business online locally. (I can recommend a company if you want.)
8) Get the money lined up
Save up if you have to. Approach potential investors and lenders - including friends and family. Figure our your financial fall-back plan. Don't expect to start a business and then walk into a bank and get money. Traditional lenders don't like new ideas and don't like businesses without proven track records.
9) Be professional office supplies / printing
Everything about you and the way you do business needs to let people know that you are a professional running a serious business. That means getting all the accoutrements such as professional business cards, a business phone and a business email address, and treating people in a professional, courteous manner.
One of the companies I recommend for this is VistaPrint, which sells business cards, brochures and a variety of other printing products like online photo albums. When I asked around VistaPrint was a company many people recommended, and I now recommend it to others too.
10) Legal and tax issues
Is what you are doing actually legal? Does your business need to be registered? Will you have to charge taxes / HST? Will you have to have Workers' Compensation Insurance or deal with payroll taxes? How will the form of business you choose affect your income tax situation? Learn what your legal and tax responsibilities are before you start your business and operate accordingly.