1. Store files correctly:

CSS and JS files should be reside under 'static' directory in the module(the rest of subdirectory tree under 'static' is an optional convention):

• static/src/css/your_file.css
• static/src/js/your_file.js

2. Add files in manifest (v7.0) or in XML(v8.0)

• Openerp v7.0 way is to add following entries in manifest (in __openerp__.py):
  ...
  'css': ['static/src/css/your_file.css'],
  'js': [static/src/js/your_file.js'],
  ...
• Odoo v8.0 way is to add corresponding record in the XML:
  • ​Add XML to the manifest (__openerp__.py):
    ...
    'data': [ 'your_file.xml'],
    ​...
  • Then add following record in 'your_file.xml':
    <openerp>
        <data>
            <template id="assets_backend" name="your_module_name assets" inherit_id="web.assets_backend">
                <xpath expr="." position="inside">
                    <link rel='stylesheet' href="/your_module_name/static/src/css/your_file.css"/>
                    <script type="text/javascript" src="/your_module_name/static/src/js/your_file.js"></script>
                </xpath>
            </template>
        ....
        ....
        </data>
     </openerp>