When I did my JulNoWriMo, I spent about a month writing notes on story and character, making sure I had enough material for a solid novel and that I knew where I was going with it. That bit of preparation enabled me to hit my daily goals easily, because I never got stuck or had to think too hard about what was next. I was able to just focus on writing the chapter in front of me, as I already had the basics worked out on paper.
If nothing else, planning can help you avoid an unexpected block halfway through!
If nothing else, planning can help you avoid an unexpected block halfway through!