I want to buy a business - where do I begin?

Congratulations! Deciding to take the step is often the hardest part. 
So what do you do first? 
Well my friend, that's a long list. 
Have you Incorporated? Set up a Corporate Bank Account? 
Have you spoken to a Lawyer or your Accountant yet? 
Have you drafted an initial Business Plan or Design Look Book? 
You should definitely get that stuff sorted and out of the way first. 

It's amazing to me how many people leave that until it's way late into a transaction.  

Do you expect a Seller or a Landlord to take you seriously if you aren't taking your own business seriously? I don't mean that to come across sounding harsh, but I promise you it's not usually well received when I tell them "Oh they don't have a business plan ready..."

You should certainly expect to spend a few thousand dollars in this "preparation work". 
Once you've done this a few times, you'll likely have the confidence to do a lot of it yourself, but if it's your first rodeo don't eff around.

As an illustrative example, Landlords will base your required security deposit on how comfortable they feel leasing a property to you. 
If your business plan looks like you made it in 5 minutes and your "marketing plan" mentions advertising in the Yellow Pages, you can bet you'll be paying a significantly higher security deposit. You might think that doesn't seem like a lot, but then you likely won't be shocked when your deposit is set at 6-12 months Lease amount. In Vancouver, that could easily be $70 -100,000.
Spending a few more days, or a few hundred dollars for someone on Fiverr to do some graphics work for you is a wise investment.
If you don't know where to begin with a Business Plan, here's a link to