Don't panic. Don't bang your head against the wall. (All you get is a headache... trust me on that.) Writer's block requires a thoughtful, logical approach, so hating yourself will go nowhere.
The first thing we tend to do when we have writer's block is to leave the book. We close the file or notebook and say we'll get to it later. Well, sometimes that works, but sometimes we still haven't touched it a week later. Or a month later. At that point things get a little worrisome. That's why I've compiled this list.
1. Try taking a walk or bike ride. Sometimes you just need the time to yourself. I know you've probably heard this before, but that's because it works. Let your mind drift to your characters, and an idea may arrive.
2. Think about your book before you go to sleep. Sometimes you dream about it, which can provide ideas. Sometimes you figure out the answer to your writer's block before you fall asleep. (If you're like me, you'll grab the nearest Post-it, scribble down your ideas, and then stay awake until late at night contemplating them.)
3. Ask a friend or family member for an idea. My dad is very helpful sometimes. Once my mom gave me an idea for an entire book.
If you have someone who knows your story well, they can offer a lot of ideas and insight, as long as you catch them when they have time to talk. (Try asking during a long car ride, while the person is cooking supper, etc.)
4. Keep an idea notebook. Fill it with random ideas (new antagonist, different setting). You can also write down your dreams in it, and scribble down prompts when you think of them.
5. Go people-listening. Inconspicuously eavesdrop on conversations at the mall or grocery store. What bothers them? What everyday trials do they endure? Sometimes the best ideas come from random places.
6. Write. Write something. Write a paragraph about nothing, or use one of the prompts I have below. Sometimes paragraphs about nothing can be very entertaining, because they bring out your unique voice.
7. Do you know much about history? History is full of fun tidbits. Read a history book and watch the dramas of the past unfold. Events based on historical events tend to be very realistic. Just don't have the Germans come conquering London and killing all the people of a certain race, or people will roll their eyes at you. (Also the Germans may be offended.)
8. Do you keep a journal or a blog? Your deviantART journal will work! It's full of ideas on everyday life.
9. Write down what you want to write (for example, I need George to go there, and meet up with them. Meanwhile, Emily should be off helping out with preparations...). This technique can be really useful, and it helps you think logically about your objectives.
10. Ask someone nearby a hypothetical question relating to your book. (What would you do if______?) Try to avoid letting the person suspect anything, and try to suppress the urge to run off cackling if you come up with a particularly evil idea.
11. Read some of your favorite books and watch some movies. What do you like about them? What do you dislike about them? How could this information apply to your story?
12. What is your theme? Try adding a short scene to emphasize it. If you don't know what your theme is, make a list of moral ideas that show up in your book and try to come up with something. Then bring out the idea through your book, and consider new events that it might generate.
13. Edit what you've previously written. You're being productive, and you're thinking about your book. Seriously. It's a really good idea.
14. Do you know about Myers-Briggs? Google "Myers-Briggs free" to take a test. It's a personality test, and while having your main characters take it isn't necessarily productive, at least it involves your book.
15. Besides considering your theme, try to think if there are any specific points that you want readers to notice (for example, your antagonist is trying earnestly to fix things but it just isn't working). Make a list. Now consider how you could modify (or add...?) scenes to bring up these points. Be careful when adding scenes: don't interrupt the flow of action.
16. As you did in 15, make a list, but this time let it be of minor characters. How well do you understand them? What are their motivations? Do your readers know them well enough, or do they need a few more lines or some more attention?
17. Revisit your previous ideas. Were there any plot twists you were considering? Did you write down any ideas that might be useful to achieve your current goals? Could any events/thoughts/feelings from your personal experience give you a similar effect? (inspired by sumgie1
18. Fill out a meme or something relating to your characters. Minimally, it'll keep them on your mind.
19. Listen to music that reminds you of your book. (suggested by That1PersonUForgot
20. Make a list of everything you could be doing to rid yourself of writer's block.
...This one doesn't seem to be working...Prompts
So that you can be writing something
1. A genius has invented a robot with artificial intelligence. That means it is capable of making its own decisions! Try writing in the POV of your lovable new robot. It and its inventor could make quite the dynamic duo. If you'd like to research, try artificial intelligence and Asimov's 3 laws of robotics.
2. Where are you right now? Describe the area in vivid detail. Use your most colorful adjectives.
3. It's just a normal day... in the life of a dragon. Where does this dragon live? Does he/she have a family? Perhaps your dragon goes to princess-napping school.
4. Once upon a time, there was a ninja who started a ninja school. Unfortunately, this ninja was evil. He would kidnap children to train as ninjas. One day, a young ninja is sent out to kill someone who is trying to destroy this organization. Then she finds out that this person is her twin sister...
5. Who likes stereotypes? I don't! Let's throw some out the window! Write about a family with eccentric characters (a gothic girl, a skateboarding underachiever, a computer genius) who defy their normal stereotypes and pleasantly surprise the reader.
6. An alien goes to school, disguised as a human. The alien may be completely clueless and make tons of mistakes. For a twist, try putting off the realization that the character is an alien until the end.
7. Try writing a parody of the usual prince-rescues-princess idea that Disney seemed to love in the 20th century. I've tried it; it was very entertaining.
8. Write a story centered around two friends and a lucky penny.
9. Imagine the future and try writing about it. Perhaps your older self is a character. Don't forget the part about being rich and famous after you solved your writer's block!