Here are three quick game book writing tips:
Write Every Day - Put something into the project every day. Skip as few as possible. Make sure you open the file, write some new words down, and just get things flowing. You'll delete a fair amount later during editing but it's easier if it's already down. Better to put a bad idea down now just to get something written than to wait for the perfect idea later.
Copious Notes - Write down why you did things even if you aren't sure if you'll need it later. That way in a few weeks when you see the note you won't think, why did I do it that way? Delete these at the end, or save them in a side file for when people ask. But you won't regret having them and might regret not having them.
Outline First - Write the whole outline, and then fill in the blanks. Seriously, this is the best way I've learned to write. Copy the outline down into the main file, and start writing.
Bonus tip: Off site backup. Have one.