"Plans are useless; planning is indispensable," according to Dwight D. Eisenhower, then Commander of the Allied Forces in Europe during WWII. Now, you may be in total agreement with the first part of that statement, but you are really not convinced of the truth of the second part.
Carrying on with the example of a coffee shop, a business plan consultant will figure out what the best location would be. They already know coffee shops do well in areas with a certain demographic in place. These include students and workers, who are within close proximity to book stores.
If you know all of these except for Marketing, say, then this is where you will need to invest some time and effort. You can find a wealth of information by utilizing the traditional data sources such as chambers of commerce, major cities' websites, trade associations, the US Census Bureau, trade journals, magazine and online articles and advertising, etc. Performing keyword searches on Google, or Ask will bring up websites to check out. Following are some places to start:
There are a number of ways of going about the process of writing a good business plan. One of the most tried and time tested ways that works well is using a business plan template.