In my last writing post, I talked about some things to look for when you're revising a book. Those were big-picture things that mostly have to do with fixing the overall structure and plot of a book. You'll probably need at least two more rounds of revising and editing, especially if you're a beginner. An experienced author may be able to combine phases, but until you get a really good sense of how a book comes together, I recommend doing one pass that covers the structure of the book and the plot, another that drills down into scene structure and then another that deals with the words.
Once you think the plot as a whole works, it's time to make sure you've got the right scenes to tell your story. You may have corrected a lot of problems in that big-picture pass by eliminating the scenes that don't contribute to the plot, making sure the scenes aren't repetitive, or combining scenes to tighten things up. For the scenes that remain, here are some things to look for:
*Is there conflict in each scene? That doesn't mean fighting or bickering, just some sense of tension or struggle, either external or internal. In each scene, some character should be trying to get or accomplish something, and that shouldn't be easy.
* Have you set the stage? I'm really bad about forgetting physical details, so this is something I usually have to add in revisions. Where is the scene taking place? How does this place look, smell, sound, feel? How does that affect what happens? For instance, if the scene takes place in public and the characters are talking about something that should be a secret, that should affect the way they behave -- furtive glances to see if anyone's eavesdropping, keeping voices low, reacting if the other person speaks too loudly, etc. Are there any environmental conditions affecting the characters? Are they hot, cold, wet, smelling something nasty, bombarded by noise? That will affect the way they behave -- acting grumpy because of discomfort, rushing through things because they're eager to get away.
* Do the characters have emotional reactions to what's happening? This is another thing I usually have to add in revisions. Unless your character is a robot, there's probably going to be some emotional response to everything that happens. The level of response will depend on the magnitude of the event. Quite frequently, the emotion will trigger a physical response -- heart rate speeds up, hands shake, that sick feeling in the stomach forms. There can also be an emotional response to a setting -- is it a comfort zone or something that makes someone edgy, like a claustrophobic person in an elevator. Think of the traits and background you've given your characters and make sure they're responding in appropriate and consistent ways. Doing this can add tension and conflict to a scene.
* Are you using subtext? This is really tricky but can be incredibly effective. People don't always say what they really mean in conversation, and the more emotional or important the subject is, the less likely they are to address it directly. For instance, a lot of fights in relationships are over seemingly petty things, but the fights really aren't over who took out the trash last. They're about underlying issues. There may be a contrast between the dialogue and all the nonverbal communication like body language, tone of voice and positioning, and then the emotional response may also tell the story. You get a more interesting scene when the characters aren't directly saying exactly what they mean and convey their real meaning some other way. The point-of-view character may or may not pick up on the subject, but it should be there for the reader.