Many entrepreneurs start working from home and use a part of their apartment or house for their business. You should inform your landlord about your plans. Also contact the Amt für Wohnen und Migration, the municipal Housing and Migration Office, whether you are actually allowed to use your home for business purposes or whether you need a permit to do so. If you are a home owner, you should also obtain approval for working from home in case of doubt.
You also need to consider building, fire protection, and industry-specific regulations such as requirements for practices and rooms in which some form of childcare is offered, or food hygiene regulations for anyone planning to store, process or sell food.