Following are some of the important points/Best practices that should be taken in consideration while creating a new custom module in drupal.

1)   Use underscore “_mymodule_” for private function.

2)   Use “ l() ” instead of “<a>text goes here</a>”.

3)   Avoid writing all the coding inside a single module file, instead of that you can use .inc files and include them.

4)   Use hook_form_FORM_ID whenever possible.

5)   Don’t Mix Business PHP code & HTML (Use theming)

6)   Avoid Using “SELECT *” in query, instead use “SELECT tablename.*” or “SELECT alias.*

7)   Avoid Using SERVER variables ($_GET, $_POST , $_SERVER etc), use DRUPAL API

8)   Use Proper Formatting.

9)   Add Relevant Comments (file, functions, blocks).

10)  Put hook_(un)install, hook_enable, hook_disable and hook_schema in .install file

11)  Use placeholders for query arguments.

12)  Use theme(‘image’, …) instead of <img … /> tag.

13)  Constants must be written in UpperCase.

14)  Module constants must start with MYMODULE_. (modulename)

15)  Do not use “prefix” & “suffix” with form elements, use theme function (drupal_render()).

16)  Include files only when necessary (include_once, require_once, drupal_add_js, drupal_add_css).

17)  Remove unused code.i.e Avoid using Dead Code

18)  Follow best practices (content type, views, features) = Don’t reinvent the wheel.

19)  Avoid Using Pure PHP code, use DRUPAL API.

20)  Ensure Permissions are properly used in hook_menu and hook_permission

21)  Use tpl files instead of theming functions when writing more than 10 lines of HTML.