If you have large background images, make sure that they are in 'jpg' format. If you have music files, make sure that they are in 'mp3' format. If you have multiple classes that are only different by their images, find a way to use only one class for all of them. If you have multiple classes that are only different by one or two other states, use field values to differentiate between them using a single class. If your sprite images can be reduced in size by removing only transparent pixels, do so. If you have multiple subclasses of a class with similar code in all of them, remove the similar code from the subclasses and put one copy of the code in their superclass (same with field declarations). If you have any unused image or music files in the 'images' or 'sounds' folders of the project, remove them.