Since I've been asked at least once a day for the past week whether or not I'm doing NaNoWriMo, it seemed like as good of time as any to post on it. I posted on this topic last year, and I still encourage you to remember that there are alternatives if you want an activity that will challenge you as a writer.
Here's the short answer: I'm not doing NaNo. Mainly because my daily minimum word count is pretty close to the 1667 words per day NaNo requires already. I am a writer. Writing things is my job. I don't get paid if I don't write the words. (And since I'm a writer at the early part of my career, the ratio of words I write but don't get paid for to words I do get paid for is still fairly high. Certainly high enough that I'm not about to start another project without a better reason than "all the cool kids are doing it.")
But since at least some of the people who have asked me if I am doing NaNo are actually asking whether I think it's a good idea for them to do so, here is my longer answer, in the form of musings.
I think anything that challenges people to try something new, something they thought was maybe too hard, or maybe a little bit scary is a good thing. If you want to write a novel, and participating in NaNo is the boost (or the kick in the ass) you need in order to do that, well, why are you asking me what I think? Sign up, and write. Make your word count. Finish, and be proud of yourself.
The other thing I like about NaNo is the word count requirement is a good way to help people turn off their internal editor. It vaccinates against writeritis. There just isn't time to think, not if you want 50,000 words in 30 days. Sometimes it's necessary to stop worrying about the writing, and just tell the story.
Here's what I don't like about NaNo: 50,000 words is not, in most genres, a publishable novel. In fantasy, the genre I write in, 50,000 words is approximately half a novel (standard manuscript length is 100K, plus or minus ten percent.) Maybe you already know this - I didn't, when I started writing - and are planning to use November to get the skeleton of your story down, and then hang muscle and skin on the bones later. Maybe you don't care about professionally publishing, and just want to have the experience of telling a story.
But if you do have professional publication as a goal, you will have to add in those 50,000 or so words before that becomes an option. You will have to seriously revise the 50,000 or so words you did write during NaNo, because turning off the internal editor might result in the completed skeleton of a story, but it can also result in some really rubbish prose. You'll need to do these things before you query agents, because once an agent has turned down a project, even if it's just because your word count was too low, you don't get to query that agent with that project again.
Still, if you really want to write a novel, don't ask me if you're ready. Don't ask that question of anyone but yourself. When the answer is yes, and you're wondering how to do it, well, do whatever it takes to put your pen in your hand or your fingers on the keyboard every day, and write. And good luck.