Keep an eye on your Employees
Select and hire employees. This can be done on the basis of experience, knowledge or age. For example, an older employee will retire earlier, but will have more experience. So choose wisely. In the beginning, you only need mechanics and a bookkeeper, but as you level up, you can also hire technical managers and HR managers to automate some of your tasks. This will allow you to focus more on the most important tasks that earn you your money.
Make sure your employees are happy, get enough sleep and reschedule your employees if one of them gets sick. You will also have to deal with holiday requests from your employees. If you don't do this or not on time, your employees will become angry and you have the chance that they will resign. If that happens, it will cost you extra money, because you will have to recruit new employees again.