I'm not trying to be funny (okay, maybe just a little witty), but I truly believe the secret to writing a book is to sit your butt in a chair in front of your computer and just write.
Like any normal person in the universe, I have suffered from writer's block. And it stinks. It's a nagging little voice in your head constantly reminding you that you are behind in your writing, yet this is precisely why it is so hard to start up again. You've lost the flow. You know that the next chapter has to be based on the last but you've completely forgotten where you left off. Or, you're stuck on character development or progressing the plot and you just can't see any way around it. It can all become quite overwhelming.
So I say--don't do it. Don't review your last chapter and certainly don't look at your notes. Instead, just open up your last saved file, find a section that needs writing, and start to write. And you'll be amazed at what happens. Suddenly you'll look at the clock and notice an hour's gone by and you've written four new pages! You'll be filled with exuberant joy and leap out of your chair to dance around the room to celebrate your invincibleness. Why? Because you just advanced your book by four pages and that is something to celebrate.
The whole idea behind the concept of "just write" is to trust your mind. Sure, you may not remember a character's name, but you remember the major action he's supposed to do, so just use a question mark as a placeholder for the name and keep writing. You may also forget a city name or the colour of a character's hair, but that's okay too. Just keep writing. In my experience, it's more important to write something than nothing at all, and you'll be amazed at how quickly the story line comes back to you. After all, the details are still in your creative brain somewhere, just snoozing in the murky grey matter until you enliven them.
Remember, a full page of writing is easier to edit than a blank one.