Template:TemplateModuleTreeSimple

mymodule/* contains php pages (note that you can also add any other subdir of your choice). Note: If your module is a metapackage (a module that will embed other modules in same zip, you must put here a file metapackage.conf)
mymodule/build/ can contains any file you develop for compiling or building package
mymodule/core/modules/ contains module descriptor file modMyModule.class.php
mymodule/core/triggers contains triggers provided by module
mymodule/admin/ contains pages to setup module
mymodule/class/ contains PHP class files provided by module
mymodule/css contains CSS files provided by module
mymodule/js contains javascirpt files provided by module to add new functions
mymodule/docs to provide doc and licence files
mymodule/img contains images files provided by module
mymodule/langs/xx_XX contains language files for language xx_XX (try to put at least en_US)
mymodule/lib contains libraries provided and used by module
mymodule/scripts to provide command line tools or scripts. Note: Command lines script must start with line #!/usr/bin/env php
mymodule/sql contains SQL file provided by module to add new tables or indexes
mymodule/theme/mytheme if module provide its own theme/skin