I've been developing a business plan since before the pandemic started.
Realistically I won't even be able to start operating unless I have excess time and money. I am coming upon such a scenario, and I'm honestly frightened by the prospect that I will have to put my cajones where my mouth is and I might fail (waste thousands of dollars).
I've been an operations person for a while, and I know several people that have started a business, and have had nominal success. So my opinion here isn't unfounded, though I have no success to speak of myself.
BASICALLY: You have decide/determine what you are going to do. Innovate and or mimic.
I would say the most businesses in general, especially SMB opt to mimic for the bulk of their business model, and attempt innovate in some way on the margins.
Having innovation being the core of your business venture, to start, is expensive, and risky.
To mimic another business that you know already works functions, is a matter of knowing how and why it functions.
No need to reinvent the wheel with an auto-shop, but you can certainly mix up your offerings and services on the side to try to wring out more productivity or profits.
If you're trying to sell an innovative mouse and keyboard setup that is convenient for a airplane, then you would have to spend a lot of money in R&D, manufacturing prototypes, and figuring out the marketing for something new in the world nobody knows about.
I guess the only other thing I would add is that you should layout all the processes that the business does, quantify these processes in terms of costs and returns, legal proceedings, labor needed. Then just get the inputs and outputs of these processes mapped out relative to customer experience.
There a whole other conversation to be had about what business you should choose to mimic, but you ask general advice so yeah.
Also read books..