Think of driving a car - if you dont know where you are going you could end up anywhere, or simply driving around in circles.
If you run a business, not having a business plan will leave you going round in circles. It does not have to be a 40 page glossy brochure - but it needs a clear overall purpose - e.g. to provide a professional tiling service that generates enough income to make a living. Simples. lol!
Once you have the overall purpose - you must decide "how will I achieve this?" this is where you set out your objectives. Again - this does not require an MA in Business Studies, but basic straightforward ways of achieving your purpose in an objective manner - e.g. :
1. To obtain and maintain basic equipment to do the job professionally at minimum expense.
2. To set out a pricing/quotation framework that ensures that the income generated covers the business running costs, and pays me a living wage.
3. To market my business to ensure a steady flow of work is generated.
You can undoubtedly add a few more....
Once you have decided your objectives - decide (a) how you can achieve them (b) when you want to achieve them by (c) what a successful outcome looks like (how do you measure your objective?) (d) if you cannot sort out a,b, or c is there any point to the objective - is it realistic? (e) write specific things down that need to happen to achieve that objective (e.g. objective 1 might include "buy a van,").
Now, as a matter of course in deciding what the purpose of your business is, and what the objectives are, it follows naturally that you will have some ideas of where you want to be in 1 year, 2 years, 3 years etc. (e.g. to break even in year 1 is a good plan!).
And in a nutshell you have a business plan. Now I know there are a lot of people out there saying "I just want to be a tiler" and thats fine. But if you want to run your own business - you want to be more than just a tiler, and you need to put some thought into what the business needs to be successful, or you will go bust pretty quick.
Oh, and finally, you need some contingency plans - e.g. what happens if I break a leg (e.g. how will I pay the mortgage then?) or what if it snows during the "barbeque summer" we are due this year?
None of this is highbrow quantum physics and there is nothing to fearfrom doing your own business plan - you can pay someone to do it for you - but the best person to decide what the business should be about - is the person actually running it!
Good luck!