Many will agree with me: writing is the easiest part of the book.
But what comes next? As a writer, you're basically a loner, withdrawn in the world you're creating. That means, you will have a book finished that you had in your head,
every single character, the storyline, the development is close to you.
Question is, is it any good? What do others think of your writing? To get a decent feedback, you need others to give you an opinion. Best would be to not ask friends or family as they are inclined to praise the book you've worked so hard for, and they don't want to hurt your feelings.
There are several online-communities that provide the comments we need. There, we might get pointed out the holes in the plot-development, where we went wrong with the characterisation, etc. With the right advice, we're able to edit our novel until it's ready to submit to agents and publishers. Editors, nowadays, are very selective people, so are agencies.
Another new site, http://authorsonshow.com/, gives authors and their ready-to-submit manuscripts the opportunity to showcase their story. Alongside this platform runs a blog with similar features.
But, there's more to it. This site also has a publisher, an agent, and reviewer, who answer questions from the readers, and successfully published authors are posting their experiences in publishing.
There are videos, informations and advice about writing on AOS as well.
So, I'd recommend to have a look, make suggestions and become part of something good.
Have a nice weekend, all.