Set up role permission

First, add this to \mod\your_module\db\access.php (after line $capabilities = array( )

    'mod/your_module:view' => array(
        'captype' => 'read',
        'contextlevel' => CONTEXT_MODULE,
        'legacy' => array(
            'teacher' => CAP_ALLOW
        )
    )

Open \mod\your_module\lang\en\your_module.php, add this line:
$string['your_module:view'] = 'View your module';

Change version.php to new version, and then goto Notification.

Use this to test the permission:

$context = get_context_instance(CONTEXT_MODULE, $cm->id);
has_capability('mod/your_module:view', $context)

Construct a url string

new moodle_url( 'url_path', array( 'paramenter1'=>$value1 ) );

Make new module with groupING

In mod_form.php, add this line:
$this->_features->groupings = true;

Note: But i still wonder why others module don't add this line but they are still available for groupING, any idea?

Add a table to Module Database

1. Site administration -> Development -> XMLDB editor
2. Find your module and click [Load]
3. Click [Edit]
4. Click [New table] and fill in the detail
5. Click [Back]
6. Click [View PHP code]
7. Select action: create table
8. Select table: select your table name
9. Click "View"
10. Copy the code to mod/your_mod/db/upgrade.php
11. Change XXXXXXXXXX to new version number (e.g. 2011022301)
12. Open mod/your_mod/version.php, change $module->version to the new version number
13. Notification 
14. Done

Add a field to Module Update page

By Module Update page, i mean the page shown when you add a new activity or update it.

Note: You should add a field to the database first if you want to save the entered field information.

1. Open mod\your_mod\mod_form.php
2. Add this line: $mform->addElement('text', 'your_field', 'label_shown', array('size'=>'64'));
3. Done

Note2: your_field is the field name in the database of table mdl_your_mod, the field information will save to the table

Note3: To show the field, just use $your_mod->your_field

Add a field to Module Database

1. Site administration -> Development -> XMLDB editor
2. Find your module and click [Load]
3. Click [Edit]
4. At the Tables section, click the table you want to add field
5. Click [New field] and fill in the detail
6. [View PHP code]
7. Select action: add field
8. Select field/key/index: your_new_field_name
9. Click "View"
10. Copy the code to mod/your_mod/db/upgrade.php
11. Change XXXXXXXXXX to new version number (e.g. 2011022301)
12. Open mod/your_mod/version.php, change $module->version to the new version number
13. Notification 
14. Done

A good way to print message

Use: print_string( 'the_message', 'your_module_name' );

Then, at mod\your_mod\lang\en\your_mod.php, add:
$string[ 'the_message' ] = 'Welcome!!!';