Fortunately, there are ways to help with this.
- Plan it out. What's going to happen next in the story? Where is the scene going? What happens from this point on? If you plan ahead, you'll have an easier time writing the scene. You'll know what direction you're headed, so you'll have a good idea of how to write the scene.
- Cut it. Maybe the reason you're stuck on this scene is simply that the scene isn't doing you any good. Is it adding anything to your story? Does the scene serve a purpose? Is it pulling its weight? Will you just end up cutting it during revision? Then maybe you shouldn't bother getting through it, and should just delete it.
- Backtrack and rewrite. Go back through your novel, and find the last spot that worked for you. What was the last good point before you got to the scene you're stuck on? Try again from here. Rewrite the problem scene. A few wording changes might do the trick.
- Take a short break. The keyword here is short. If you're stuck, get up and walk around. Make yourself some cappuccino. Do that biology worksheet you've been procrastinating. Go for a run. When you come back to your writing, you might have found some new inspiration. This one can get dangerous, though, because once you start that break, it'll get harder and harder to get back and do that scene.
- Troubleshoot the scene. Just why, exactly, is that scene not working? Maybe something is out of character, for your MC. Maybe it just doesn't fit the story. Look closely at the scene, and figure out why you're stuck. Once you've determined the exact problem, it shouldn't be hard to fix.
- Expand your trilogy into a 4-book "cycle". But only if your name is Christopher Paolini.
Some people would tell you to skip over the scene and continue writing, and return to it later. I disagree with this. By skipping over the scene, you are ignoring a problem that has a good chance of snowballing into a much larger and harder problem to fix. If there's an issue with that scene, and you skip it, the issue isn't going to fix itself.
Besides, if you skip that scene and keep writing, it's going to get much for difficult to go back and finish the scene. You can't just wait for the inspiration to hit you, because that might never happen. You have to be proactive about getting through these trouble scenes. Because, as said by Jack London, "Don't loaf and invite inspiration; light out after it with a club.”
How do you get yourself "unstuck"?