AngularJS best practices for module declaration?

‘Best’ way to declare a module

As angular is on the global scope itself and modules are saved to its variable you can access modules via angular.module('mymod'):

// one file
// NOTE: the immediately invoked function expression 
// is used to exemplify different files and is not required
(function(){
   // declaring the module in one file / anonymous function
   // (only pass a second parameter THIS ONE TIME as a redecleration creates bugs
   // which are very hard to dedect)
   angular.module('mymod', []);
})();


// another file and/or another anonymous function
(function(){   
 // using the function form of use-strict...
 "use strict";
  // accessing the module in another. 
  // this can be done by calling angular.module without the []-brackets
  angular.module('mymod')
    .controller('myctrl', ['dep1', function(dep1){
      //..
    }])

  // appending another service/controller/filter etc to the same module-call inside the same file
    .service('myservice', ['dep2', function(dep2){ 
    //... 
    }]);

  // you can of course use angular.module('mymod') here as well
  angular.module('mymod').controller('anothermyctrl', ['dep1', function(dep1){
      //..
  }])
})();

No other global variables are required.

Of course it depends all on preferences, but I think this is kind of the best practise, as

1. you don’t have to pollute the global scope
2. you can access your modules everywhere and sort them and their functions into different files at will
3. you can use the function-form of “use strict”;
4. the loading order of files does not matter as much

Options for sorting your modules and files

This way of declaring and accessing modules makes you very flexible. You can sort modules via function-type (like described in another answer) or via route, e.g.:

/******** sorting by route **********/    
angular.module('home')...
angular.module('another-route')...
angular.module('shared')...

How you sort it in the end is a matter of personal taste and the scale and type of the project. I personally like to group all files of a module inside of the same folder (ordered into sub-folders of directives, controllers, services and filters), including all different test-files, as it makes your modules more reusable. Thus in middle-sized projects I end up with a base-module, which includes all basic routes and their controllers, services, directives and more or less complex sub-modules, when I think they could be useful for other projects as well,e.g.:

/******** modularizing feature-sets **********/
/controllers
/directives
/filters
/services
/my-map-sub-module
/my-map-sub-module/controllers
/my-map-sub-module/services
app.js
...

angular.module('app', [
  'app.directives',
  'app.filters',
  'app.controllers',
  'app.services',
  'myMapSubModule'
]);

angular.module('myMapSubModule',[
   'myMapSubModule.controllers',
   'myMapSubModule.services',
   // only if they are specific to the module
   'myMapSubModule.directives',
   'myMapSubModule.filters'
]);

For very big projects, I sometimes end up grouping modules by routes, as described above or by some selected main routes or a even a combination of routes and some selected components, but it really depends.

EDIT:
Just because it is related and I ran into that very recently again: Take good care that you create a module only once (by adding a second parameter to the angular.module-function). This will mess up your application and can be very hard to detect.

2015 EDIT on sorting modules:
One and a half year of angular-experience later, I can add that the benefits from using differently named modules within your app are somewhat limited as AMD still does not really work well with Angular and services, directives and filters are globally available inside the angular context anyway (as exemplified here). There is still a semantic and structural benefit though and it might be helpful being able to include/ exclude a module with a single line of code commented in or out.

It also almost never makes much sense to separate sub-modules by type (eg. ‘myMapSubModule.controllers’) as they usually depend on each other.