The reason that Safe Haven made me think of this, is because the antagonist in the story, Kevin, always has an amazing internal dialogue. Nicholas Sparks is an outstanding writer--I mean, for getting a $1,000,000 advance on a first novel, (The Notebook), I suppose he should be. You understand what Kevin is feeling. The run-on sentences work, because you know that Kevin is angry, and he hates his wife who ran away, but he still loves her...but hates her, but loves her. You feel the character.
I remind myself constantly when writing to think about how my character feels. Consider what you would actually be thinking about if you were in their situation. What if you were a wife that ran away from her husband? How would you feel? What would you be afraid of? Nicholas Sparks feels his characters, so when he writes them, you feel them, too. This is the key to the kind of writing that readers immerse themselves into--the kind of writing that takes you to the scene, that makes you stay up until 3:00 in the morning to find out what's going to happen. This is the kind of writing that you want to write.
In short, my tip of the day is to pretend that you're an actor/actress. Become your character. What would they really do? What would they say? How would they feel? Put yourself in their position. Feel the snowflakes melting on your nose when your character walks through the first snow of the year. Taste the sweet sugar on the outside of a donut when your character eats it, and feel the pain when they lose a loved one. Become your character, and your prose will be strong, and your reader will believe it. Your reader believing your words is so important, because without it, you're phony, and your characters are cardboard.