We're writers, so it's going to happen sometime (and probably many times). In fact I think it's plagued not only novelists, but any kind of writer, whether it be a reporter, journalist, poet, screenwriter, student with an essay, etc. Our muses like to hide sometimes and usually it takes a great deal of effort to unbury them. So I've come up with a few things that help me overcome this affliction. Maybe it can help others, maybe not. You don't have to be some famous big-shot author to struggle with this. It happens to anyone!
Generate excitement. Share your ideas with other people and their enthusiasm will rub off on you and suddenly you'll be pumped to write. Other people are great ways to revive your writing spirit. You just shared it with your friends, you can't just not write it now!
Read something of yours. Usually when I'm drowning in the depths of one project I feel like my writing is ugly ugly ugly brain vomit and that no one would ever possibly want to read it. But I've found that it's not as bad as I think. Once I'm able to take a step back and observe it after a few days, I see the shine that I missed before. Of course it can still be polished up, but at least for me, I think, "Wow, I can't believe I wrote this. It sounds better than it did before."
Read something else. I love this one. If you just can't crack into your writing piece, read something instead. Always the second best alternative because it can help get those creative juices flowing just reading someone else's work.
Write a random drabble. These are really short works, and they can be on any topic. I encourage you to write about something you usually don't write. I personally like doing fanfiction; there is a certain standard about this. The characters are already set in stone. Everyone knows who they are, so this gives you the chance to slip into that character and explore them a little bit better. This can help you later when you return to your writing, as oftentimes a big part of writer's block is losing your voice or not being able to connect with the characters or settings.
Find other sources of inspiration. I use music to set the tone sometimes when I'm struggling with certain scenes, or I seek out art work if I can't picture something exactly right. If you can't generate ideas or if you feel like your story doesn't have enough substance, I usually turn to movies, tv, or books, and look at how they did it. Those people know how to craft something with an engaging beginning, middle, and end all while handling well-rounded characters and usually great settings.
Identify the source. Why are you feeling writer's block? Is it because you don't have any ideas? Maybe you've hit a bump; you know where you want to story to go but you just don't know how to fill in the pieces to get it there. Perhaps it's not that at all, and the words simply won't come to you. There are tons of different reasons people can get blocked, and identifying it can really help you overcoming it. If you don't know the problem, how can you hope to fix it? Once you know what it is, focus on that.
Take a break. For me, I get burnt out on writing because I constantly write. Every single day, more than 4,500 words. Can you comprehend how much that is? Sometimes slowing down and taking a break is necessary. Disconnect yourself from writing and everything related for a brief amount of time and you can come back refreshed.
Try something new. I found that continuing on the same series one book after another drains me so bad. I have tons of other ideas for other series, so I decide to work on those a bit, which makes my creative mind feel fresh and flexible. Even if you don't have enough ideas for another series yet, try fleshing it out a little. Just the smallest break can really help.
That's it for now. Please let me know if they helped!