So you have completed your first draft of your novel! Congratulations!! This is a huge accomplishment and should not be taken lightly. Few set off on the challenge to write a book. A good number of those that try it don't make it. So, take a little pride in this accomplishment. :)
Now the bad news. It is not near good enough to publish. I'm sorry, but no matter how careful you are, it will have mistakes, lots of them. But don't worry, this is normal and happens to everyone on their first draft.
It is time to edit your work. There are times when I love this process and times when I hate it. The refinement and improving feels good, but the tedious of it can get to me.
How does one go about editing their work? Read your book. That's right. You just finished writing it, you have not thought about anything else, but now you are going to read it. Not only that, you will probably read it multiple times.
as you read through your work, you should be looking for different things. You might even read it with one goal in mind and then read again with another, and so forth.
Things to look for:
Weird 'flow' (stories should flow nicely from paragraph to paragraph and chapter to chapter)
How many times should you go over your book? One author (I wish I could remember who) recommended reading your story ten times. My patience has never let me get past four times. Still, the more you read the better the book will be.
One other extremely important step is to get yourself a proofreader. I am always amazed at the number of mistakes exist AFTER I've gone through the book multiple times. You need a second set of eyes. This person does not need to be a professional, but should be someone who can pay attention to detail.
Fortunately for me, my wife is an awesome proofreader. Our process is that I print out a copy of the book (she likes to mark up the physical pages) and she gives me the chapters as she finishes them.
Each person is different, but I would recommend letting the person have as much time as they need. Proofreading is not reading-for-fun. It takes some time to do it right. Give the person the time they need (if you are paying them, then maybe you push a little).