What Johanna said ^
Additionally, if they are on different pages, there are two methods to move them. With the apps wiggling (careful not to touch the cross or the iPad will think you want to delete the app) drag the selected app to the edge of the screen. The page will move to the next home screen, and you can drop it where you want. Don't drop it on top of another app, otherwise a folder will be created, containing both apps.
If this doesn't work well for you, drop the app in the dock, at the bottom of the screen, move to the required page and drag the app out of the dock. You can have up to 6 apps in the dock, rather than the default number of 4.