Magento 1.x Best Practices and Conventions

[Gabriel Guarino]

Hi everyone,

I would like to share with you the best practices and conventions for Magento 1 that I've been implementing for the last 7 years.
I will be editing this answer with more and more information, and I would like to hear more about your best practices and conventions.

Based on your participation on this topic, I will edit this post in the topic and I will add your best practices as well, so we can use the first post as a "wiki" and improve it with the collaboration of everyone in the forum.

Back-end

1. Do not modify the Magento core: app/code/core
   
   This is the #1 rule when it comes to customizing Magento. To be specific, the files from the app/code/core folder should never be modified to ensure the stability and upgradability of the Magento store.
   
   
2. Avoid rewriting classes
   
   
   
3. If you rewrite a class, then annotate the changes you made to the core file
   
   
   
4. Avoid implementing a lot of observers
   
   
   
5. Keep a small number of shopping cart and catalog price rules
   
   
   
6. Remember setting magento in Developer Mode to develop
   
   
   
7. Develop with the display_errors setting enabled and E_NOTICE turned on
   
   
   
8. Always turn off the cache in your local machine to avoid losing time
   
   
   
9. Document your classes and methods using PHPDoc comments
   
   
   
10. Limit the usage of PHP in the front-end
    
    
    
11. Do not use direct SQL queries to connect to the database, use models instead
    
    
    
12. Follow Magento naming conventions for classes, methods and files
    
    1. Methods and variable names should use camelCase
    2. Indexed arrays should use snake_case keys
    3. PHP variable names in the front-end should start with $_ (underscore after $ sign)
       
       

Front-end

1. Don't use inline CSS in the front-end
   
   
2. You can use tables, but only if you want to present tabular data
   
   
3. Use image sprites to load icons in your theme

[magento_wire]

Agreed post..!!! related to the Magento 1.x best practices and conventions.

Thanks for sharing the detail and make us updated