Don't start writing your novel until you know your characters very, very well. What they'd do if they saw somebody shoplifting. What they were like at school. What shoes they wear. Spend days - weeks, months - being them until they thicken up and start to breathe.
You need to know the characters as living, breathing people before you start the plot; otherwise, you'll feel panic, anarchy and chaos.
Once a character has gelled it's an unmistakable sensation, like an engine starting up within one's body. From then onwards one is driven by this other person, seeing things through their eyes ...
Writing a novel is a huge adventure; when it's going well it's more fun than fun. When it stutters to a halt put it aside. Go for a swim, go for a walk, take a week off. Don't panic or be afraid; you and your characters are in it together. Trust them to come to your rescue.