An example of a bad practice in Magento 1.x is directly modifying the Magento core. Some developers do this instead of creating custom modules, which results in changes in the platform that are not visible in the code base through the custom modules. This will prevent those features from being migrated to Magento 2, since they are not visible to the developers when they review the custom modules.

If their core has been modified, then that will be the first step: moving those changes from the core to custom extensions, and restoring the original core files from Magento.

You can download any version of Magento, 1.0 onwards, from the Magento Tech Resources downloads page at https://magento.com/tech-resources/download.

The software engineer will be able to compare the current state of the core of your store with the original Magento core.

Another bad programming practice in Magento is placing business logic in templates instead of custom extensions. The right way of adding business logic to templates in Magento is adding that logic in blocks in custom extensions, but some developers include PHP code in frontend templates instead.

The software engineer should review the frontend templates to see if there is any custom business logic that needs to be moved to custom extensions.

I don't recommend having a lot of third-party extensions. You should have just the ones that you need and that you consider essential for your store.

That said, you should review whether the third-party extensions from your store are available for Magento 2. This means that you should go to the website from the module vendor and check whether a new extension has been created for Magento 2.

It's very important to mention that some module vendors are creating a version of Magento 2 for their extensions, but those extensions for Magento 2 don't have all the features from the extension for Magento 1.

This means that you should not only check whether the extension is available, but also whether all the features that you use in Magento 1 for that extension are available in the extension for Magento 2.

If an extension is not available for Magento 2, then you should analyze whether you really need that extension. In case you need it, you can contact the module vendor to see if there is a planned release soon. If the module vendor is not planning to release a new version for Magento 2 soon, then you should create that extension from scratch for Magento 2.

If you were looking for a custom feature in Magento 1 but didn't find any extension in Magento Connect, then you had to implement custom code to support that extension. These are custom extensions that are available in Magento 1 but that are not compatible with Magento 2.

Magento 2 is a new platform with a new data structure and new coding practices. You should create a new version from scratch for those extensions with compatible code for Magento 2.

Are there unused custom or third-party extensions? If that is the case, you should review the features from those extensions to see if you really need them. By reducing the number of extensions, you reduce the amount of code to migrate and you keep a cleaner Magento 2 instance.

Custom JavaScript is not migrated to Magento 2 and you need to take note of the custom features that you implemented using JavaScript. Those features should be manually migrated by an experienced Magento developer to Magento 2 to use RequireJS.

Now that you have analyzed the code, it's time to review the migration requirements. Sometimes, the original requirement changes after the code audit. That is reasonable since you will have more information about the current state of your store and you will create a plan of action based on that.

After the code audit process, you will have a list including:

There is something else to consider--the theme. The theme is not automatically migrated from Magento 1 to Magento 2. Just as you did for the third-party extensions, you should review whether the theme is available for Magento 2 and contact the theme developer, if necessary, to see if there is a planned release coming soon.

If you want to keep the same look and feel for your store, then you should consider that the theme should be created from scratch for Magento 2 if the theme is not available for the new version of Magento.

Now, the plan to move ahead with the migration should be similar to the following: