Maybe you take a long walk, and let yourself get bored to clear your brain, and let a new idea come to you. Maybe you take a nap or listen to music that makes you jump around and then start fresh afterwards. Maybe you reread earlier parts of your work-in-progress, looking for a nugget of information that can -- indeed, should! -- be expanded. Maybe you read another book to consider how other authors dealt with similarly thorny plot dilemmas...
Or maybe you Just. Keep. Writing. Sometimes the risk is too high that, if we walk away to "refresh" ourselves, we may never come back. And in November, any writing you do to help move your story forwards does count towards your final word count goal. Go ahead, do a little free association! Maybe indulge in some character development, writing short scenes that you know will never make it into the final draft, but that nevertheless help inform your own sense of the characters, and perhaps help you see the next (plot) encounter these characters will have. Write that backstory or give the character a crazy dream sequence. It all counts towards your 50K, and it gets you into the habit of working through the tough moments.
And don't forget the NaNoWriMo forums! Don't know what your character would do next? Get online and ASK someone! Join a word war, find a writing prompt, let someone else name that character you're currently calling "Bad Guy #2." Or just go moan to a crowd of sympathetic ears who will all encourage you to get back in the saddle. Writing need not be such a lonely endeavor, at least not next month...
Obviously, sometimes a break from writing really is called for, but I think that beginning writers often take too many such breaks, waiting for that romantic AHA! moment where the plot is suddenly laid out before us like a freshly paved highway. Sometimes, you just have to keep plugging away. As Stephen King says, you have to build good habits so that your muse knows when and where to find you when the time is right.
And in November, it's all good. Every dumb word you write gets you one word closer to your NaNo novel. And your odds of writing one good page in the midst of several bad pages are infinitely higher than your odds of finding a good page on your desk when you didn't write at all that day, because you were stuck, or had writer's block, or weren't feeling it.
When inspiration hits, by all means grab it and milk it for all it's worth! I have twice started my NaNo early because I think the spirit of NaNo is to write more, and I wasn't going to let a great idea get away because of a fun-but-artificial start date.
But if inspiration doesn't hit? Keep writing anyway. You will never know what you are capable of creating if you don't keep going over those rough spots.