I recently came across this neat online tool: a free grid generator.
http://incompetech.com/graphpaper
Scroll to the bottom of the web page to find different styles for Chinese and Japanese character guides. Click on your preferred style, then enter your specifications (such as line weight and color), and voilà! You have your very own character-writing paper to print out, and you can practice to your heart's content.
How about other tools for improving your character writing?