We don't perfectly understand the way the creative subconscious operates, but we know or suspect a few things that you can use to your advantage. Keep these things in mind while you're drafting new pages, and you might make it easier on yourself to produce on command.
Negatives Might Be Invisible
There is some evidence (though it's inconclusive) that the creative subconscious doesn't respond to negative statements. Words like "not" might slip right through without registering. If you do affirmations or meditations as part of your creative ritual, make sure you phrase it positively. So,
I will not get distracted
would be better phrased as,
I will stay focused.
I won't pause until I get to my goal,
could be converted to,
I will write steadily until I reach my goal.
Positives Are, Er, Positive
Even if you don't do this type of affirmation work, pay close attention to how you think about your own creative process. Use positive words -- not just words that avoid "not," but words that cast your concepts in a positive light The creative part of your mind is open to suggestions, and you don't want to teach it to behave in accordance with whatever negative statements you put on yourself. You may despair that your ideas are all misshapen abortions, but you don't want to convince the deepest part of your psyche that this is a true statement. Even the heaviest self-abuse can be spun around into something more positive and less self-destructive. Those misshapen abortions might be better thought of as tiny seeds. Some will sprout, and the others can remain fallow, but you don't have to insult them. Or their mamas.
This is all very Pavlov's-dog, but it turns out that certain kinds of ruts are very good for our creative minds, though we tend to call them rituals. You may have already experienced something like this in your own writing life. Do you always begin a new writing session by pouring a fresh mug of coffee? Do you light a candle? Close your web browser? Play a particular song when you're writing certain characters or scenes?
These things can function as triggers -- external, physical cues to the internal psyche that it's time to shift into productive, generative work now. If you have trouble settling down to work, try incorporating something like this and see if it makes it easier to get started.
Create Safe Zones
When we were talking about our timed writing exercise, what we were essentially doing is creating a type of safe zone. When you set the timer, you made a bargain with yourself. For ten minutes, you were free to create new words without any interference. That ten minutes was a safe space. Nothing was allowed to damage it.
There are other ways to create safe zones. Your desk might be a physical safe zone if nobody else is allowed to use it. Or maybe it's your entire office. If you are in a busy family household, you might make "after bedtime" into a safe zone for your writing by turning off the tv, ignoring the laundry, and setting the phone on vibrate -- in another room. Or you might get up before everyone else and treat the silent dawn as a safe zone.
Some writers have one computer for goofing off online, household tasks, the checkbook, and so on, and a separate computer used for writing and nothing else. I used to use my laptop this way until a certain 9-year-old appropriated it for games. But for me, while it worked, it worked exceptionally well. Powering up that laptop was all it took to get me into a productive, calm mindset.
NaNo itself is a safe zone. Think about it. :)
Use the Clock
We've already discussed timed speed-writing as one way to use the clock. But there are more such methods. Morning pages are one: Every morning, no matter what, the very first thing you do straight out of bed is write a set number of pages. They can be journal pages, manuscript pages, or whatever you choose, but they have to be first thing in the morning.
I think it was Dorothea Brande (or Brandt?) who advocated a second session later in the day. She suggested that once the morning pages habit was established, you should pick a set time every day for a second writing session. No matter what else you're doing at that time, stop. Write for a set period. Don't stall or dawdle. Set an alarm clock if you must, and avoid "lemmejust" syndrome -- "Lemmejust finish reading this email; lemmejust fix a snack; lemmejust retie my shoelaces." The time is the trigger. Once that second session is routine, she advocated changing the time from day to day. By doing this, you can train yourself to generate new pages on command.
The Connecting Factor
All of these tactics share a single underlying concept. We can train ourselves to be both more creative and more productive by using props like affirmations, special coffee mugs, clocks, candles, music, and so on. What you choose to use is far less important than its constant usage. Your goal is to create associations -- a positive affirmation sets a goal, and 9:00 p.m. means it's time to write, and Eric Clapton's "Slow Hand" means you're writing in your antagonist's point of view. Once the association is established, the generative part of writing should get much easier.
So what rituals do you use to signal that it's time to write? Do you use different triggers when you're editing?