Writing is a solitary endeavor, and unlike other occupations--whether or not you've done a good job is not always obvious. Oh, you might think it's good stuff, but doubt lurks in the back of your mind. Many times, as you write your book, you may feel like you'll never finish. You might wonder if what you've already written is any good. Maybe it's crap, and you're just too dumb to know it?
If you show it to family and they like it, you might wonder if they're saying so just to be nice. Heck, even if you show it to strangers, you'll wonder. This is where self-confidence comes in. If you have it, great. If you don't--fake it. Tell yourself, this is good. Again, this is good. Because how can you expect anyone else to like your stuff, if you don't?
While you don't want to be arrogant, or be tooting your own horn all the time, tell the world, "My book is really good."
My book is really really good. It has romance, suspense, humor, and sexual tension. It's called, Risky Romance. This isn't a prod for you to buy the book, cause it's not published. I don't even have an agent yet, but I will. I'm confident of it.