After a while, you become so familiar with your own writing, that you cannot see the issues with it. When I first showed a friend my writing, I thought I was handing in a perfect manuscript, totally flawless. In fact, it was littered with problems - overuse of adverbs, misuse of words, grammatical mistakes... the list goes on.
I am so glad I decided to show my writing to this friend before entering it into a competition. The manuscript I eventually handed in was much stronger than the original and it did really well!
However, I do think you need to be careful. Once you have got opinions from others, you need to make sure you don't just change everything unless you absolutely agree with it. At the end of the day, it's your work. But then again, if people see big issues in it, then what's to say publishers won't?
Good luck!
