I strongly despise cover letters, because they are so ......unhelpful and often just plain silly. Some people prefer them, so just here are a few hints to keep them from making those who read it nauseated. I'll add some of my thoughts when I see these comments. Your goal is to have a MATURE approach as compared to a silly one.
"I'm a very fast learner." ---totally meaningless and nobody believes it
"I passed all my classes with flying colors." ---okay, so the training you got must not have been very good. I don't want someone who passed with flying colors. I want someone who went to a very tough, challenging course and STRUGGLED and was successful IN SPITE OF how hard it was.
"I'm exactly what you need." ---I'll be the judge of that, and I am not interested in anyone who pretends to know exactly what I need.
"I love your company and that's why I applied to work for you." ---No, you don't and you didn't. That's really silly.