1. Unless you are truly wanting to write a story for giggles, do not plan to fail at the start. There will be plenty of time to pull plot out of places you shouldn’t be shoving plot into, but the first two weeks are not that time. Leave the carnivorous sentient couchs and the broom handles that want revenge until you absolutely cannot salvage what you have on the page.
2. Plan, but do not overplan. Before you start, you should have a character in a world with a problem. This is true for any novels. Think of the AIs that were smart enough to look at the overwhelming odds against them with all the orcs and turned and ran. You do not want your characters to look at the massive iceberg. All they need to see at the beginning is that tiny bit that floats. The more your story goes along, the more they try to fix it, the bigger the problem gets. Have a general idea of what you want to have happened by the end of the story too, then send the main characters out to solve their own problems.
3. If a salesman’s mantra is ‘always be closing’ the author’s mantra has to be ‘always be escalating’. Each scene should change one problem at the end of it. So many unpublished books out there have a great beginning and an awesome ending and absolutely nothing changing for twenty chapters while the characters just muddle around the middle. If you’re bored with what’s happening on the page or if your characters are just standing around and talking, it’s the perfect time to make the worst possible thing happen and have them deal with the new problem as it exists now. If they’re looking for a guy who can solve the problem, kill him. If they need X to solve Y, have X not work. Have the secret entrance into the castle be fixed.
4. Make sure your main character isn’t the best/brightest/smartest/richest person out there. If you’re good guys are only succeeding because the bad guys are just that dumb, that’s not exciting to read. Books are about the main character but the bad guy has to be a match enough to cast serious doubt in the good guys succeeding. In Greek legend, Heracles’s name literally translates to Hera’s glory. There needs to always be a real threat that your main characters can and will fail.
5. Don’t write if you’re not feeling it. This is the opposite advise than what most nanowrimo’ers will tell you, but before you should sit down to write, you should have in your mind exactly what this scene is going to accomplish as a goal in the scene itself and how that is going to affect the plot as how it stands. It just so happens that a good length for a scene is around 1500 words, and you need to write 1660 words a day to reach your goal. Every scene in the story is a micro-short story with a beginning, middle and end. So within that scene, you need to set up what the problem is, what the main characters are going to do to fix it, and what the outcome is of their attempt, for better or for worse. If you plan to write one scene per day, your story’s pretty much set. If you do not know what you’re going to write about, don’t waste your time at the computer. Go for a walk, have a shower, play a couple games putting the “what has to happen right now?” question in the back of your mind. When you have to work through the rising and falling action with a climax within that scene, 1500 words isn’t going to seem like enough words to pull off all that that scene needs to do to change one point in your plot.

Bonus point:

Don’t follow a synopsis off a bridge. The more you write, the more your subconscious can take over. If you have no idea why you’re writing something, don’t sweat it. What you put in as a throw-away line can be the defining moment in chapter 23. I’m a skeptic at heart, but there is a magic to story telling where events that seem utterly unrelated can come together in a perfect moment of syzygy. Don’t try to control everything. If a plot point doesn’t come together of if that thing you thought was going to be the cornerstone of everything doesn’t seem to do anything or go anywhere, you can always delete it in the rewrite.

Bonus, bonus point:

You’re not going to be writing anything that just needs a dramatic “the end” before it gets sent off to New York for the fame and fortune you so richly deserve, but this is going to give you the clay in which you are going to need in order to make the second draft obvious that you knew the whole time how this story was going to end. When you rewrite it, don’t look at the words on the page as something that just needs to be polished, look at them as a stepping stone. No matter how much you preplanned, the characters on the page aren’t really going to feel real until you’ve stomped around in their boots for a while.