The first person a writer often shows his or her work to is a friend or family member. Before you do that, read on to find out why it's a bad idea.
When you are editing a book, one of the absolute worst things you can do is to give it to someone you love to read it. Big, BIG mistake. While letting someone you know and trust read your book is easier on you, it is not conducive to the editing process. You won't always get honest feedback or an accurate review.
One reason for this is that it doesn't matter what the person says about the book, they will no doubt be first and foremost concerned about hurting your feelings. They don't want you to think that if they don't like your writing it means that they don't like you. In fact, this person is going to do everything they can to truly LOVE your writing. They don't want to hate it any more than they want you to think they hate it. This beer-goggles-of-sorts bias is a quick way to ruin any chances you have of getting accurate feedback.
Another reason this is a bad idea is that most of the times your friends and family already think you are a wealth of information on whatever your chosen topic is. You could be completely BS-ing them and they wouldn't know the difference. While it can be comforting to think that everyone regards you as a genius, it would be a far worse shock to learn from your readers that you're not, rather than from a respected editor or literary reviewer.
A third reason that this is a bad idea is that as hard as it is to give criticism to people you know, it is just as hard, if not even harder, to take it. When you take criticism from people you know personally, it can feel as if they doubt your knowledge and intelligence. After all, you just spent all this time creating your masterpiece and they took one read through it and tossed it back at you as if it were cold soup coming from the kitchen. Even if your book is lacking in grammar or content, learning this from a trained professional is much easier to stomach than hearing it from family and friends.
For new writers, friends and family seem to be much more abundant - and less expensive - than professional editors. Don't let that keep you from having your work reviewed by a thoughtful eye. Check online for websites and discussion boards set up just for this purpose. Even if you find out that your mother was right, you owe it to you career to employ a third-party.