OK, so sitting around waiting for inspiration doesn't work very well. Sure, every now and then you get that "Bing!" and you sit down and bang out a few thousand words of whatever. But personally, I have a bunch of partially done stories on my hard drive that have been sitting there waiting for inspiration to get past whatever rough spot I ran into years ago and I'd really like to have some other way to deal with them.
Paying attention to what was going on with my writing through November, I saw three reasons for having writer's block. One, which hit in the middle of the month, was that I personally just felt like crap for reasons unrelated to my writing. The second reason is that I didn't know what to do next. I'd hit a point in the story where I didn't know what the next scene should be, or I needed a new major subplot if this thing wasn't going to end up wrapping at short story length rather than novel length. And third, I knew what I wanted to do but I couldn't quite figure out how to do it, at the word-and-sentence level.
The first problem is one I can't solve for anyone else. Heck, I can hardly solve it for myself. I'm bipolar, so just waiting a while will improve things eventually when my brain chemistry shifts. In the middle of NaNoWriMo, watching ten days or so go by with nothing at all getting written just added to the depression, but it did eventually clear up and I got going again. I think the only advice I can give here, though, is to be aware of what your problem is. If it's something unrelated to your writing, you might have to clear that up before you can get back to being productive on your story. Assuming you're not at the level where you need medication, some common suggestions include sun light and exercise. Both at once is cool. Lack of natural light can encourage depression in some people, and getting outside during the daylight, or getting a full-spectrum lamp, can help with that. Exercise encourages the production of endorphins and speeds up your metabolism. Journaling (the private kind) can help as well; writing down what's bothering you a word at a time can help straighten out the sludge in your head and help you work out what to do about it. If none of that helps and you're still feeling upset or depressed, I can only mimic Ann Landers and suggest talking to a professional.
The second problem is more manageable. Not knowing what to do next in your story is a common problem. Unfortunately, there are a lot of common solutions, most of which are crap IMO. Particularly when you're doing NaNo, you get a lot of suggestions which are designed to build your wordcount rather than actually help your story move along as a story. Adding and killing characters at random, throwing in aliens or talking rocks just for the heck of it, or other such random plot-movers might well give you something to write about if you're stuck, but to me they don't actually solve the problem. When I finish a story I want to have something I wouldn't mind posting in public with my name on it, and that's not going to happen if I find myself staring at a collection of random stuff stuck together with duct tape.
What I discovered did help was going back to the plot level and analyzing what was going on, what I wanted to happen, and what the obstacles were. The first time I did this I started out writing a letter to aleathiel, since we were reading each other's NaNos and passing help and encouragement back and forth. Explaining to someone else, in writing, what was going on, what I wanted to have happen and exactly why I had a problem, what I'd thought of as possible solutions and why they wouldn't work, etc., ended up being a solution in itself. Before I actually finished I'd come up with a solution to my problem and I was able to keep on writing without having to actually send Alea the letter. I tried it again recently with a speed bump I hit in Hidden Magic and it worked again, so I think I have a winner here. The trick is to be addressing the ramble to some other person, even if you don't intend to send the letter; if you're talking to someone else then you have to explain, completely and explicitly, all the things that you yourself "just know" and it can help you find holes or snags or ideas you didn't know you had.
Specifically, when I go into this level of analysis, I go back to the basic plot. Who's the protagonist? What does he want? Why can't he have it? What does he do to try to get it anyway? That's your plot, right there. That's every plot ever written. The protagonist wants something -- that's the goal. The reason why he can't have it is the main obstacle; there might be more than one, especially in a longer story. What he does to try to get it anyway is most of the story, the action, the bulk of the verbage. The climax comes when he either overcomes the final obstacle and achieves his goal, or when he realizes or accepts that he can't have it or doesn't want it after all. The denoument or wrap-up is where loose ends are tidied and the reader is shown why all this was significant, if it wasn't made plain earlier -- did the protag change somehow? Did the situation change? Was there something to learn? It doesn't have to be long or involved or sophisticated, but there should be some sense of closure and completion for the reader.
So when I run into a problem, I look at where I am in terms of the plot. What am I doing and how does it further the plot? How does it help the protag try to achieve his goal? What obstacle is the current scene working on? Is it a plotting problem, a character problem, a pacing problem...?
Have I gotten side-tracked into some activity which is irrelevant to the plot? If so then it should probably be cut out -- if I particularly like it then I can save it in a separate file and make some use of it later. Alternatively, I might be able to think of some way to use it and make it a sub-plot. If the protag's main goal is to get into his new neighbor's bed but his dog just ran away, maybe I can make his neighbor a dog lover -- I can let him see the protag out looking for his dog and come help and they can strike up a conversation. Much better than meeting at a singles' bar. :)
Have I created a problem too big for the protagonist to solve? Maybe he needs help, or maybe I need to break the problem into smaller chunks, or maybe I could have the antagonist make a mistake. (Although you have to be careful with this last technique -- no one's impressed when your protag knocks over a straw man.) Sometimes looking back at your protag's goal can help you redefine your win condition. In my NaNo novel (which still doesn't have a name) I've got my protag living in a very conservative, rigidly moralistic society. If he wants to be free to be himself (a gay man) and find someone he can love and live with happily (another man) then he basically needs to overthrow the government and change the world views of millions of people, to create a society where he can do his thing without being harassed or arrested or "treated" for his "condition." Clearly that's not going to happen; it's not at all a realistic goal. But does he really need to go that far? Maybe I can come up with some other way for him to achieve his goal of living happily with his chosen partner without actually overthrowing the government or converting a few hundred million people to benefits of enlightened compassion, the latter being the more difficult goal BTW. Maybe instead of changing his country he could find somewhere else to live. Leaving his country is about on the level of defecting from the old Soviet Union, so it's still a goal worthy of a novel, but it's achievable whereas the first goal wasn't. (And I can file that "overthrow the government and change everyone's view" goal for later, in case I decide to turn this into a series of novels.) OK, so now I have a slightly different problem, one that'll be difficult but solveable. Onward.
Or maybe the problem is too small -- you see this in a lot of published novels, where the whole book would only be six pages long if the main characters would just sit down and talk like intelligent human beings for a few minutes. One thing to keep in mind is that the easier your problem is to solve, the shorter your story should be. Longer stories need more difficult and complex problems to support them. Stretching your story out by making your protagonist into an idiot isn't a good technique, although a lot of people use it. Note that this can work when done with humor, if you mean for your protag to come across as an idiot, but humor is tough to do well and it's one of those things that either works all the way or doesn't work at all.
The third possibility is that I know what I want to do but I can't quite come up with the words. This is a situation where the classic NaNo advice, "Write it now, edit it later," can work. It can be tough if you're not used to banging out a lot of placeholder text, but if you can grit your teeth and force yourself, you can put down the bare bones of the action and dialogue and get through the problematic scene and go on with the story. You can come back later and dink around with the bones, add some flesh, cover it with skin, maybe do something fancy with makeup and costuming. But the bones are the important part; they're what you'll attach the next scene to. So you might end up with a chunk that looks like: So Joe cleans up the basement, working around Bob's car, and while he's cleaning he's thinking about their last argument and realizes that he was looking at the situation from the wrong POV, that Bob didn't really mean he should kill all his guineapigs, that he just wanted their cages cleaned more often and maybe moved out of the kitchen.... Etc. That gets the important stuff down and you can go back and polish it later.
Some people can just skip a scene and go on and write a later scene, then come back and write the earlier scene later. I can't do that, myself. If I end up twisting the earlier scene a bit, if I think up something new or cool to do with it, or get some inspiration that makes the story take a hard left right there, then that means everything I wrote which is chronologically "after" that earlier scene is useless, and writing large chunks of stuff to throw away annoys me. I mean, sure, it happens, but I don't have to go encouraging it. :P
The trick, though, no matter what the problem happens to be, is not to let things Just Sit for too long. My subconscious does a lot of work when I'm writing a story and sometimes walking away for a while does help. But I've found that if my subconscious hasn't solved it for me in a day or maybe two, then leaving it alone any longer isn't going to help. At that point it's time to sit down and just write, dammit. Whether I can whack myself on the head and get right back into writing on the story, or whether I have to sit down and write a letter to myself to explain exactly what the problem is and why this or that won't solve it and just keep going until I find something that will solve it, or to talk out loud about it, or to talk out loud to someone else about it, or whatever ends up helping, I have to actively work on the story. Just ignoring it and waiting for "inspiration" to flash doesn't work.
A novelist character in a book once said something like, "There's no such thing as writer's block, there's just writers who don't feel like working today. When you're a full time writer with bills to pay then you sit your butt down every single day and do the damn work. That's all there is to it." This is loosely paraphrased off the top of my head, but it gets the gist across. And I think to a point she was right. We hear about inspiration and "the muses" and all, but when it comes down to it the writer is in charge and it's all about whether you feel like doing the work today. And if you have a problem, then "the work" for that day includes figuring out what it is and how to solve it. It can be difficult, yes, and frustrating, but finally getting past that roadblock and seeing your story moving again is a very satisfying feeling and worth working for.