1. Once you have finished the first draft of the novel it’s helpful to leave it for at least 2 months, but up to 6 months, so that you can be more objective when reviewing it.  
2. Read the entire book quickly to get an overall view of it. You want to get an idea of how well the plot works and whether the main character(s) is sufficiently likeable and entertaining to keep the reader interested in him or her. Is there enough conflict to make the reader really invested in what is happening? Correct any errors you notice and write down anything larger you see that needs to be fixed.
3. Read the book again slowly, carefully checking the book for errors of punctuation, spelling and grammar. At some point you might also want to read the book aloud as this can help you see if the sentences flow well and it gives you a different perspective of the manuscript.
4. Go through every scene and make sure it works. It should only stay in the novel if it is action (moving the plot forward) or reaction to something that has happened. There should be constant conflict in the novel: in a romance the conflict will be largely emotional; in a thriller there may be an antagonist threatening the main character or his/her family. Whatever type of novel it is, the reader has to feel that the stakes are high, that the main character’s happiness or even life is at risk.
5. Make sure every scene conveys its setting. Where and when is it taking place? What does it look like? What sounds, smells and sensations do the characters experience? Does it affect their mood? Setting can often be used to add to the conflict in a scene, for instance by having a woman who desperately wants a baby in a playground surrounded by children, or a noisy background making it almost impossible to have an important conversation.
6. The characters in the scene should be shown clearly. What does their body language say about their moods? Is their dialogue convincing and unique to their character? If you are showing the scene through a character’s point of view – which will usually be true – how do their personality, mood and thoughts affect what they are experiencing?
7. If the plot feels dull at any point, introduce a twist, such as a new obstacle the protagonist has to overcome, or a new character who causes conflict to the protagonist. If the plot feels forced and unnatural anywhere it is probably because you are making the characters act in a way that is unconvincing in order to move the plot in a particular way. Think about how you can nudge them in the right direction in a realistic way, such as putting someone they love in danger.
8. Make sure the antagonist is as complex as the protagonist and has as strong a reason for what he/she is doing as the protagonist has. The antagonist should have a good motivation, no matter how terrible it is. Can you give the person a horrible past that gives the reader a touch of sympathy for him or her? A fully rounded character is far more interesting than a Disney-style baddie.
9. If your main character doesn’t seem sufficiently sympathetic you could gradually reveal a painful past. You can also make the protagonist likeable by giving him/her a moment away from his/her own problems to help a vulnerable person or animal. If there isn’t enough tension, think of ways to increase the conflict, such as a betrayal, someone dying, something important being lost or the protagonist having an accident at the worst possible moment. If there are chunks of exposition that slow the book down, find better ways to gradually reveal the information, such as through dialogue. If your book has a theme, make sure it is clear.
10. Read through the manuscript one final time and check once again for general mistakes and overall plot and characters. Correct any problems.

At this point you will want to find others to read the book to give you feedback on it. My article on deciding what editing help you need gives advice on this.