[header] How to cross your eyes [title] Focus both your eyes on the tip of your nose. [step] Slowly lower your gaze until both of your eyes are focused on the tip of your nose. This may cause a bit of an eye strain, since you're probably not used to using your eye muscles this way. 
Though you won't be able to see it yourself, your eyes should now be crossed. But this is no fun so far--since you're looking down, no one else can see that your eyes are crossed.