The appropriate logo
The logo should in any case be stylistically in line with the product or the client, respectively. In order to guarantee that, the first step is to get an overview of the copmany. You should do that already before the briefing takes place.
"In line with the product or client also means this: It's no use developing a highly professional logo for a hot dog stall. The logo's beholder would instantly notice that something's not right, which casts a damning light on the client, and consequently on the designer.
It is difficult to find symbols for service businesses or their services / "products". In this case, abstract shapes are frequently fallen back on.