Aside from graphic and logo designing skills, a logo designer requires some other skills as well.
If the designer does not have good communication skills, he will fail to understand what the customer wants and this could be a huge problem since it is the base of the design process. Sometimes, people tend to take a double meaning of a single sentence and start assuming things on that basis. A professional logo designer will know what the customer wants to say and will understand his words. He doesn't just need the communication skills for understanding the client but also because he needs to be able to explain to the client his design process and his ideas for the logo design. There can be situations like when the client wants something to be a part of the logo design but the designer knows that it will ruin the design or it doesn't suit the company image so the designer must be brave enough and have good skills in order to explain and convince the client that the idea is not a good one. If there are some trends or cliche's in the industry that the client wants the designer to use for his logo as well, the designer should tell him, without offending him, that they will ruin his design or that the design will look tacky, if done so.
Before the designer begins the design process, he must have a picture in his mind of what the client wants and if it will be versatile and will look good or not. The ability to see and judge before having produced it, is very useful as it saves a lot of time. Although, he will not have every little detail in his mind, it is still important to at least have a rough sketch of it. Designs and design trends keep changing and coming back; the designer should be able to judge whether a certain design trend will come back or is just going to fade away. They should also be able to judge if a certain trend can be safe to use for a clients' design or not. "Thinking outside the box" would be a great skill to have as well. This could enable designers to create something new and make it into an everlasting logo.
The client will obviously provide the designer with the extensive details about the company but it is up to the designer to research more on the company. Because even if the client has given him everything he could, he still cannot give an outside look of the company as a normal customer would. And it is necessary to know how the company is viewed by its customers so that the logo will be designed accordingly. There are also other things that he needs to research on like the various trends of logos and the types of logos that are being used by the clients company's competitors.
A designer should have adapting skills as well. In this ever-growing and ever-changing environment, it is necessary to be able to adapt to your surroundings. This does not mean that the designer should follow and design according to the trend. Rather, it means that the designer shouldn't stick to one design style and play it safe but he should be comfortable to experiment with various styles and get the best possible output.