Follow a strict rule:
In writing, there are rules and guidelines on how to go about it. However, what a writer should never do is follow a strict rule on how writings should be done. As a writer, you should be free to break the norm, find your path and do what works best for you.

Write like someone else:
Yes, it is good to have a mentor or a writing idol; however, what you should not do is to write like someone else; because in that case, you would never be the best, rather you would be the second best. So, be free to find your own voice and style and write like yourself.

Give up:
Although writing is tasking, it can also be very rewarding. So when writing becomes tough, take a break, re-strategize but never give up. Just keep writing until you become the very best.

Read more at: http://www.thereadywriters.net/10-things-a-writer-should-never-do/