It is a given that newcomers to any profession, hobby, or endeavor will make mistakes. The question is how you deal with those mistakes. It is what's done with those mistakes that gives someone the leg up as they go along to get into higher and better positions.
This goes for writers as well. People new to writing, whether it's poetry or prose, are likely to do something that's considered wrong. The important thing is to learn from those things and to use the knowledge to improve your future products.
Kristen Lamb is an author who has guided writers of all levels to success. She has written many blog posts giving advice about what writers should and should not do. One of her most recent posts is entitled 'Five Warning Signs Your Story Needs Revision'. In it she lists five of the more common errors new writers make: too many named characters, jumping right into action in the beginning of the story, strange movements of body parts, too much physiology, and too many adverbs.
These are not the only mistakes writers make. Writer's Digest, one of the top publications for writers, offers this article on the five most common mistakes. Pat Holt, who writes about books and the publishing revolution, has an article on his site that talks about ten mistakes not seen but easily fixed by new authors.
Writers must write, it is what they do. Mistakes will be made. They can be fixed with a little effort and some help from the advice given by people who have worked hard to get where they are now. Research through Google can find all sorts of things to help. It can be overwhelming and any good writer will need to discern what is right for them and what isn't.