When I first began writing, I was quite reluctant to show my work to anyone. Though I do have a close friend who reads for me, he reads not to critique, but to make sure that I have not missed any pertinent information along the way. He reads from the perspective of someone unfamiliar with my topic, and if he can understand it, then I know I have gotten my point across.
Fiction, however, is a different matter. Plot must be resolved satisfactorily, dialogue must be snappy and precise, and the writer must always be cognizant of providing just enough background information, without intruding too much on the story. Needless to say, though I still have my close friend read my fiction, I have also reached out to writers for their critiques.
I have been fortunate to connect with a number of authors, published and not, who have graciously read my work, in exchange for my critique of their work. Each one has added another layer to my understanding of writing and their words have been invaluable.
Local writers groups, online forums, even Facebook friends of the writing ilk, help to broaden your horizons. Don't ask for too much, but don't be afraid to ask. Our work is close to us, like a child or lover, and we sometimes don't see the flaws - so reach out and connect with another author. The critique you recieve could make the difference between rejection and acceptance.