Judgments are a part of life. I think the only thing you can work on is the type of judgment you make at a given time.
Judging a book by its cover is unfair because that's not what the book is about. OTOH, judging a man/woman by her looks for, instance, can arguably be a good judgment of the person (how they keep themselves).
For further study:
Judgement - Wikipedia, the free encyclopedia