Simplicity: simpler is better and easier to remember
Scalability: The logo should be still as effective when it is scaled down to a small size. A competent logo designer will be aware of this along every single step of the logo design process, and you should always pay attention to the scalability of your designs as you are working on them.
Legibility: The logo should be legible at the drop of a hat, and easily recognisable. Make sure the logotype is legible, consider things like kerning, leading, size, weights, and font pairing when designing the logo as a whole.
Relevancy: Your choice of logotype and logo mark will be the voice of the brand and so you need to understand that voice.
